CLONING OF EUKARYOTIC ELONGATION FACTOR 3 FROM PHYTOPHTHORA INFESTANS Rachael Han, Rayleen Hu, Shawn Kant, Siddharth Kantamneni, Alon Millet, Meera Sakthivel, Kush Shah, Stephanie Tang, Parisorn Thepmankorn, Alice Vinogradsky, Ronald Wang, Rachel Weinstein Advisor: Dr. Stephen Dunaway Assistant: Mitchell Dittus ABSTRACT Eukaryotic elongation factor three (eEF3) is a highly conserved ATPase essential for the survival of most, if not all, lower eukaryotic organisms. Required for the elongation process of protein translation, eEF3 is critical in aiding with the removal of deacylated tRNA from the Esite of the ribosomal complex. Found exclusively within lower eukaryotes such as fungi, but absent in higher eukaryotes, eEF3 has important implications as a future drug target against pathogenic fungi; inhibition of eEF3 would directly induce death in fungi but have no anticipated deleterious effects of any kind on host cells. In order to better understand the mechanisms by which eEF3 functions, this study presents an attempt at cloning the eEF3 gene from P. infestans , commonly known as “potato blight,” via the Gibson Assembly process. Transformation of E. coli with plasmid DNA containing the cloned P. infestans eEF3 is also detailed. However, the transformation ultimately failed due to partially degraded ampicillin, resulting in a lesser concentration of viable antibacterial chemicals, which was evidenced by a DNA smear rather than clear, delineated bands. Despite failing to accomplish the ultimate goal, possible avenues are addressed regarding future research in the realm of identification and validation of eEF3 inhibition as a potential drug target against pathogenic fungi. KEYWORDS : eukaryotic elongation factor 3, antifungal drug target, P. infestans , Gibson Assembly, plasmid shuffle INTRODUCTION Due to the omnipresence of the bacteria and viruses that dominate the domain of diseases, pathogenic fungi have largely been forgotten for the better part of medical history (1). However, over the past twenty years, the situation has changed dramatically due to the astronomical increase of invasive fungal infections, especially in the emergency room. This phenomenon can be attributed to a variety of reasons. For one, many fungi once thought to be nonpathogenic have been deemed otherwise, creating a significant reidentification crisis for researchers (1). In addition, many emergency room patients possess severely compromised immune systems as a result of intensive therapies and procedures – chemotherapy and radiation therapy [81]
for cancer treatment, organ transplant recoveries, or major surgery recoveries – that dramatically heighten the likelihood of fungal infection occurrences (1). Under such circumstances, pathogenic fungi gain easy access into patients’ bodies and have opportune chances to propagate illness. Symptoms of some of the most prevalent fungal diseases include wheezing, chest pains, vomiting blood, chills and fevers. Furthermore, in the period of time between the years 2007 and 2009, there has been a 27% increase in the demand for antifungal drugs. This notable increase is 67 times greater than the increase in demand for antibacterial and antiviral drugs over the same time frame, emphasizing the extent of the proliferation of invasive fungal infections in the recent past. Unfortunately, the mortality rate for critically ill patients with invasive fungal infections remains staggeringly high despite the increase in drug usage: current survival rates hover around 42% to 46% (1). Common antifungal treatments, such as amphotericin B, result in a wide array of negative side effects in patients that often cause new problems, compounding the actual fungal infection itself with issues such as nephrotoxicity and hepatotoxicity; side effects of amphotericin B specifically include convulsions, hallucinogenic vision, wheezing, unusual bleeding, rashes, and potentially fever, all of which naturally render doctors incredibly hesitant to prescribe the medication (2). Therefore, given the current situation concerning invasive fungal infections in the United States, as well as around the world, and the ineffectiveness of current modes of therapy, there is a dire need for a new approach to treatment or a new kind of drug designed specifically for combatting fungal infections. While there is a plethora of fungal diseases which afflict numerous organisms, one of the most destructive quasifungal diseases is caused by an oomycete known as Phytophthora infestans , more commonly known as potato blight. This plague is cause for great concern, since it targets the third most essential food source for the entire human population. About two hundred years ago, the widespread Irish potato famine of the 1840s was a very wellknown example of the ability of P. infestans to rapidly wipe out entire crop harvests, leaving little for farmers to salvage; more than one million people died and another 1.5 million fled from Ireland during the 1840s because of the sweeping famine, immigrating primarily to the United States. Fortunately, the discovery of the existence of microorganisms in the 1860s by means of the development of germ theory as well as the ensuing creation of fungicides prevented further spread of the scourge. Within the past 20 years, however, the infamous epidemic has reemerged, this time in Russia and other nations around the globe, with significantly greater resistance to the potato’s natural defenses and various fungicides, eliminating upwards of 70% of crops each year (3). The recurrence of this newer, more robust P. infestans can attribute its severity to the high mutation rate of the oomycete, which allows the pathogen to overcome many impediments, both natural and artificial (3). Since oomycetes are capable of sexual reproduction, the genome of individuals within a population can vary widely. Rapid reproduction can spread resistance genes among the members of the population through the recombination that occurs during gamete production (4). Worse still is the fact that oomycetes, when fertilized, release spores into the air, further dispersing the plague throughout crops. This does not mean, however, that preventing P. infestans from reproducing sexually would halt [82]
their genetic mutation. Earlier studies have shown that asexually reproducing oomycetes have not only high variation within a population, but also immense genomic instability; in other words, the genes can transmute rather easily, further hindering scientists’ ability to synthesize a drug to combat the disease (5). Moreover, there may be mechanisms within the potato blight that drive the rapid evolutionary changes which threaten plants and perplex many scientists (6). While this highly plastic affliction poses a serious and widespread threat to the potato crop, there may be hope for treatment through a crucial protein known as eukaryotic elongation factor 3. All organisms, from simple fungi to humans, rely on proper translation for protein synthesis. As with many other cellular processes, translation is highly complex, involving the interaction of multiple different proteins and ribonucleic acids (RNA). Of the translational proteins involved, eEF3 is one of the most important in lower eukaryotic organisms such as yeast and other fungi, and works together with eukaryotic elongation factors one and two (eEF1 and eEF2) in translation to produce viable proteins (7). eEF3 is a single peptide with an internal structure that allows it to interact with tRNA synthetases, most likely to monitor the availability of aminoacylated tRNA needed for further peptide elongation. It also interacts with deacylated tRNA in the ribosomal E site for its removal, thereby allowing aminoacylated tRNA to bind to the ribosomal A site, which in turn allows the elongation process to continue and the forming polypeptide chain to grow. The eEF3 protein Nterminus, socalled because of the end amine group (NH ), interacts with the ribosomal protein subunits, allowing it to bind 2 with the ribosome and carry out its function in translation. The carboxyl (COOH) Cterminal end of the eEF3 contains positively charged lysines, enabling it to interact with the ribosome, and acts as the main area of the protein that binds to the ribosomal subunits. Structurally, eEF3 serves another function as an ATPase and has a repeated, mediumsized domain of around 200 amino acids; such domains include the HEAT, ABC1, & ABC2 domains (Fig. 1). Furthermore, the protein also has two nucleotidebinding sequence motifs, and while its functional significance is not completely understood, the two motifs are implicated in the ATP hydrolytic activity of eEF3, which is essential for the role the protein plays in effective translation (9). Figure 1. eEF3 crystal structure. General structure of eukaryotic elongation factor 3 (eEF3) from S. cerevisiae and some of the protein domains (HEAT, ABC1, ABC2, HB) associated with it. ADP is adenosine diphosphate, ABC1/2 are ATP Binding Cassette 1/2, and 4HB is 4 Helix Bundle (8). [83]
During translation, eEF3 maintains the crucial role of governing the removal of the deacylated tRNA from the exit site, or the E site (Fig. 2). The ribosomal Esite contains the 40S subunit head and the L1 stalk, which regulate the tRNA’s presence in the Esite. eEF3 affects the two aforementioned structures, by moving the L1 stalk into a position unlocking the Esite and thus allowing the tRNA to leave the ribosome (Fig. 3). The chromodomain (residues 761869) of the ABC2 domain in eEF3 is involved in the movement of the L1 stalk. By governing the removal of the deacylated tRNA from the Esite of the ribosome, eEF3 allows for the continuation of translation, resulting in elongation of the polypeptide and eventual completion of a protein product (8).
Figure 2. Model of eEF3 function. eEF3 is responsible for the removal of spent tRNA from the E site of the ribosome, but exists only in lesser eukaryotes like fungi (8). Figure 3. eEF3 protein structure. Diagram demonstrates the position of the A and E sites relative to other structures of the ribosome. The movement of the L1 stalk from the closed to open position, and the switch of the chromodomain of the eEF3 needed for movement of the L1 stalk are represented by the arrows (8).
[84]
eEF3 is uniquely required by funguslike organisms in the translational process of protein synthesis. Ribosomes in various other low level and high level eukaryotes do not require eEF3. Serving no known function in such organisms, the protein is neither present nor expressed in upper level eukaryotes such as humans. For instance, mammalian 80S ribosomes do not require additional protein factors, such as eEF3, for protein synthesis (10). Several lower level, nonfungal eukaryotes also do not utilize this elongation factor. For example, in metazoans, ribosomes possess bound factors, not soluble factors, that perform an eEF3like function. One such bound factor is RbbA, ribosomebound ATPase, which is found in Escherichia coli (11). However, this elongation factor is required in various fungi. Ascomycete and basidiomycete yeast both possess a functioning eEF3 (10). As a matter of fact, the eEF3 in Candida albicans , a diploid fungus yeast, was even functionally conserved within S. cerevisiae , an ascomycete yeast. Constructed with 1050 amino acids, the Candida albicans eEF3 shares a 94% identity with the S. cerevisiae eEF3 in the region of the protein that contains its catalytic domain (12). Since eEF3 is not conserved in higher level eukaryotes, it is an ideal antifungal drug target as it eliminates the threat of host toxicity. Within fungi and other lower level eukaryotes, eEF3 is known to be a vital factor in protein translation, and thus cell survival as well (13). One such eukaryote is S. cerevisiae . In the current investigation, S. cerevisiae serves as a model organism to determine if eEF3 can be functionally conserved within a wider variety of species. S. cerevisiae , more commonly known as baker’s yeast, is often used as a model for more complex fungi and potentially even humans. The proteome of S. cerevisiae contains orthologs for nearly thirty percent of human genes associated with disease, making it a suitable model for studying gene expression and regulation (14). While the goal of the research performed and further detailed in this paper consisted of cloning P. infestans eEF3 via the Gibson Assembly process, the overarching question at hand is determining whether the eEF3 gene could be functionally conserved amongst a wider variety of fungi. To do so, it is necessary to determine if the eEF3 from P. infestans would be capable of functionally replacing the eEF3 in the S. cerevisiae . If eEF3 were to be conserved within these organisms, there is a potential for use in developing a more universalized antifungal drug that may combat fungal diseases without any harm of any kind to the human host. MATERIALS AND METHODS Preparation of LB Broth and LB Agar The LuriaBertani broth was prepared by combining 10 g/L of tryptone (DIFCO FisherScientific, Pittsburgh, PA), 10 g/L sodium chloride (SigmaAldrich, St. Louis, MO), and 5 g/L of yeast extract (DIFCO FisherScientific) with doubly distilled water before adjusting pH to 7.0 with 1.0 N sodium hydroxide (SigmaAldrich). LuriaBertani agar was prepared in precisely the same manner as LuriaBertani broth, but with the addition of 20 g/L of agar (DIFCO FisherScientific). Both solutions were autoclaved prior to inoculation with bacteria. [85]
Preparation of Plasmid Vector In order to create a viable plasmid vector capable of binding with the target eEF3 gene, a restriction digest on the plasmid vector targeting specific points within the DNA sequence is necessary. All reagents and materials for the digestion were acquired from New England Biolabs. After isolation of vector DNA, a digestion reaction was prepared as 25% (v/v) vector DNA solution, 10% (v/v) Cut Smart Buffer solution, 5% (v/v) XhoI restriction enzyme, and 5% (v/v) BamHI restriction enzyme for total 20 μL with ddH O. Restriction enzymes were 2 acquired from Integrated DNA Technologies (Coralville, IA). Digestion solutions were incubated at 37°C for 60 minutes. Gel Electrophoresis of Digested Plasmid Vector DNA digests were stained with gel loading dye (New England Biolabs, Ipswich, MA) for visibility and 20 μL of stained DNA were added to each well of a 1% (w/v) agarose gel. The gel was run under a 100V current for 45 minutes before the gel was extracted from the chamber and analyzed to identify the correct section of isolated vector plasmid. Recovery of Plasmid Vector from Agarose Gels All reagents and materials for recovery of plasmid vector from agarose gels were acquired from Zymo Research (Irvine, CA). Recovery of DNA was performed as per Zymoclean kit directions. DNA was sliced from the gel above UV light and weighed to the nearest 0.1 mg. Three volumes of agarose dissolving buffer were added to each gel slice and the solution was incubated at 50°C for 10 minutes. The dissolved gel was loaded into the spin columncollection tube complex and centrifuged at 13,000 rpm for 30 seconds. The flow through was discarded and 200 μL of DNA wash buffer was added. After centrifugation at 13,000 rpm for 30 seconds, the flow through was discarded and 6 μL of doubly distilled water was added to the vial. The column was moved to a 1.5 mL tube, and after a third centrifugation at 13,000 rpm for 30 seconds, the resulting flow through containing the recovered plasmid vector was stored at 4°C until further experimentation. Gibson Assembly Reaction Gibson Assembly is a process by which multiple strands of overlapping DNA molecules can be joined together using an isothermal, singlereaction method. All reagents and materials for the Gibson Assembly were acquired from New England Biolabs, and directions were followed as per the protocol given by the supplier. The eEF3 gene that was to be integrated into the plasmid vector, supplied by Integrated DNA Technologies (Coralville, IA), was divided into two sections approximately 1600 base pairs each . After the digestion of the plasmid vector, the Gibson Assembly reaction was prepared with 4 μL of the gelpurified vector, 2 μL eEF3 Gene Block 1, 2 μL eEF3 Gene Block 2, 2 μL distilled water, and 10 μL Gibson Assembly Master Mix. The reaction was incubated at 50°C waterbath for 15 minutes to facilitate the annealing of the two lab formulated DNA strands of P. infestans eEF3 gene to the plasmid, creating a completed recombinant plasmid for transfection into E. coli (Fig. 4). [86]
Growth Conditions of E. coli E. coli was incubated at 37°C in LB broth containing 50 μg/mL of ampicillin, which served as a marker and helped to determine which of the resulting E. coli colonies contained the desired plasmid.
Figure 4. Gibson Assembly concept . A schematic representation of the Gibson Assembly process with two eEF3 inserts and 1520 bp overlapping ends. Transformation of E. coli Competent DH5α E. coli was acquired from Invitrogen (Carlsbad, CA) and transformed in a 5:2 ratio (v/v) of bacteria to plasmid solution from the Gibson assembly. After pulse spinning to mix thoroughly, the bacteria was incubated on ice for 30 minutes before being heat shocked in a 42°C water bath for exactly 30 seconds. The transformed bacteria were then allowed to grow in 1 mL of outgrowth media (New England Biolabs). After 1 hour of incubation at 37°C in a shaking incubator, the bacteria was pelleted by centrifugation at 13,000 rpm for 30 seconds. The supernatant was discarded and the pellet was resuspended in 200 μL of SOC outgrowth media before being plated onto LB agar plates by means of glass spreading beads. Plates were incubated for 24 hours at 37°C to allow colonies to develop. Isolation of P. infestans eEF3 Plasmid from E. coli All materials and reagents for the isolation of DNA were acquired from QIAGEN (Germantown, MD). After development of colonies, bacteria were swabbed with an inoculation loop and allowed to grow in microcentrifuge tubes containing LB media with 50 µg /mL of ampicillin. The bacteria were pelleted by centrifugation at 13,000 rpm for 3 minutes at room temperature. After resuspension in 250 μL of Buffer P1, 250 μL of Buffer P2 was [87]
added and mixed thoroughly into the solution by inversion four to six times. 350 μL of Buffer N3 was added to each of the tubes. Tubes were inverted four to six times. The solutions were then centrifuged at 13,000 rpm for 10 minutes. The pellet was discarded and the supernatant was transferred to a QIAprep spin column by decanting. After 60 seconds of centrifugation at 13,000 rpm, the flow through was discarded and the column was washed with 750 μL Buffer PE. Flow through was discarded again and centrifuged again to remove residual buffer before the column was moved to a clean microcentrifuge tube. 50 μL of sterile water was added to the center of the column. DNA was eluted by centrifugation at 13,000 rpm for 60 seconds. Digestion of P. infestans eEF3 Plasmid All reagents and materials for the digestion were acquired from New England Biolabs. After isolation and purification of P. infestans plasmid, a digestion reaction was prepared as 25% (v/v) P. infestans plasmid, 10% (v/v) Cut Smart Buffer solution, 5% (v/v) XhoI restriction enzyme, and 5% (v/v) BamHI restriction enzyme made up to 20 μL with ddH O. Restriction 2 enzymes were acquired from Integrated DNA Technologies. Recognition sites for the restriction enzymes are shown below (Fig. 5). Figure 5. Recognition sites for restriction enzymes . A schematic of the recognition sites for XhoI and BamHI, the two restriction enzymes used in the DNA digests (13). [88]
RESULTS In Figure 6, gel electrophoresis was performed to separate DNA that was digested using restriction enzymes BamHI and XhoI. In the gel, the DNA isolated was the plasmid vector which would later be used in the Gibson Assembly to insert labproduced P. infestans eEF3 gene. Correctly isolating the digested plasmid vector is important because it ensures that the digested pieces of the vector will not once again bind to each other, and Gene Block 1 and 2 can bind to the correct sequence to create the final vector plasmid. Lane 1 and 5 contained DNA digest samples while Lane 3 served as the control, the ladder. The gel was then placed on a UV box and the visible bright orange bands were cut from the agar gel to isolate the DNA. A ZymoClean protocol was used to isolate the digested DNA from the agar for use in the Gibson Assembly. Lane 8 7 6 5 4 3 2 1 Figure 6. Gel electrophoresis of DNA digest. This figure shows a recreated image of the gel electrophoresis of DNA digest. In order to avoid prolonged exposure to ultraviolet (UV) radiation, an image of the gel could not be taken. Note the gel background is purple and the bands were bright orange due to some UV radiation. Lane 1 and 5 contain digested DNA. Lane 3 contains the marker. Bands are linearized plasmid after cutting by BamHI and XhoI restriction enzymes. [89]
In Figure 7, lanes one, two, three, six, seven, and eight contained the digested plasmid vector DNA that was purified from E. coli . Lane four contained the DNA marker which was used as a control to compare the bands from the samples. Lane five contained the undigested vector DNA to ensure that there was DNA present within our samples. Because the digested plasmid vector DNA was once again digested using restriction enzymes BamHI and XhoI, the P. infestans eEF3 gene would have been cut away and separated as the ends of the gene contain the DNA sequence targeted by the two restriction enzymes. The gel was therefore used to determine if the P. infestans eEF3 gene was present within the plasmids transformed into and copied by the E. coli , as the gel isolates DNA fragments based on their size and length. Since there is little to no chance of mutations creating a DNA fragment with the same length and DNA sequence endpoints as the P. infestans eEF3 gene, the gel ensures that the correct plasmid was transformed into the E. coli . Lane 8 7 6 5 4 3 2 1
Figure 7. Gel electrophoresis of purified E. coli plasmid. This figure shows an image taken of the gel from the electrophoresis after isolation of the plasmid from E. coli . Lane 4 contains the marker, lane 5 contains the undigested sample, and all other lanes are digested plasmid DNA. Note the existence of smears rather than clearly delineated bars in all lanes with samples (lanes 1,2,3,6,7, and 8). [810]
The results were inconclusive, as no distinct bands of DNA were formed in the final gel electrophoresis. Rather, faint smears of DNA can be seen along the entire length of the lanes. As a result, it can be determined that the P. infestans eEF3 plasmid was not successfully transformed into the E. coli or cloned, because the presence of any plasmid in the sample would have formed distinct bands on the gel. No distinct band is visible for the undigested DNA sample due to DNA shearing by rough micropipetting. DISCUSSION In this study, the question was asked whether the eEF3 gene from P. infestans could be successfully cloned into E. coli bacteria for further use. Thus, the purpose of the research project was to clone the P. infestans eEF3 gene successfully so that it might be transformed into other fungal organisms. Future studies can be conducted with the hopes of showing the potential of eEF3 as a universal antifungal drug target due to functional conservation of the protein from evolution. Initially, the DNA vector plasmid was digested using the restriction enzymes BamHI and XhoI in order to create complementary sequences on the ends of the plasmid that would allow Gene Blocks 1 and 2 to attach. A gel electrophoresis was conducted using the digested plasmid to separate the different pieces of the plasmid. The desired portion of the digested plasmid was then successfully identified and cut out of the agar by comparing the bands to the ladder under ultraviolet light. As shown in Figure 6, the first gel electrophoresis was successful because we observed the presence of bands of different lengths, allowing for the isolation of the segments of the plasmid which were 8 kb to recombine with eEF3 in Gibson Assembly. It is essential to note that an image could not be taken due to the risk of prolonged exposure of UV light to the DNA in the gel, since strong radiation like UV light poses the risk of causing excessive damage to DNA. After running a successful gel, the laboratorymade P. infestans eEF3 gene could then be used in the Gibson Assembly reaction to be integrated into the isolated plasmid vector from the gel. After the processes of E. coli growth, purification, and digestion previously detailed in Materials and Methods , a second gel electrophoresis was run to ascertain the presence and state of DNA in the samples (Fig. 7). The lanes in the agarose gel that did not contain the marker presented cloudyclear columns rather than clearly visible, separate bands. These white columns are smears of E. coli genomic DNA, indicating that the entire E. coli bacterial genome was completely digested by restriction enzymes instead of any bacterial plasmid – the intended target of digestion. The restriction enzymes cut the genomic DNA into segments of numerous varying lengths, essentially causing bands to appear all along the gel columns; this occurrence resulted in the observation of a smear. The appearance of multiple smears rather than clear, delineated bands on the final gel (Fig. 7) was at first glance unexpected considering the existence of multiple surviving colonies on the LBampicillin agar plates. [811]
In order to check if the transformation of P. infestans had successfully worked, BamHI and XhoI restriction enzymes were used on vectors that were run in lanes one, two, three, six, seven, and eight of the gel. Even when just one restriction enzyme is used on a whole bacterial genome, said genome will be cut into a broad spectrum of DNA fragments of differing sizes. In this case, two restriction enzymes, BamHI and XhoI were used; as such, there was an even wider spectrum of lengths of the DNA fragments. Hence, not a single fragment could form a distinctive band, resulting in the smearlike appearance of bands on the gel. Although a similar manifestation was visible in lane five, the reason for that appearance is different. The DNA run in lane five was undigested, so the restriction enzymes could not have cut it into different lengths. Therefore, there is a high possibility that the smear in lane five was due to the shearing of the DNA during micropipetting, which occurs when the micropipette is handled too roughly. In addition, genomic DNA is much larger than plasmid DNA, so it would be more prone to being sheared inadvertently through micropipetting. Large, undigested fragments of DNA are fragile and will not remain intact after being disturbed rapidly, such as when the contents of tube are mixed after micropipetting by moving fluid in and out of the micropipette. The result of such actions is DNA shearing, which is evident in the gel column lane five (15). One potential explanation for the aforementioned phenomenon is the possibility that the plasmid containing the ampicillin resistance gene and the P. infestans eEF3 gene simply integrated into the bacterial chromosomal plasmid. Horizontal integration in bacteria and archaea alike allows for the movement and transfer of genetic material without descent. The integration would have rendered the transformation attempt ineffective, allowing the bacteria to survive on the ampicillin plates without the original vector plasmid. If purification of the vector plasmid was attempted, there would be nothing to purify. In practice, however, this integration occurs with sufficiently low probability for it not to be the only cause nor the principal reason for the observed result. Another feasible reason for the lack of defined bands in the gel is the potential for nonfunctional or expired reagents, resulting in the failure of the plasmid isolation protocol. This conjecture is also highly unlikely considering the reliability of commercial DNA isolation kits. In addition, these specific kits were subsequently tested in another study, and the results confirmed that the kit was fully functional and had no contamination. The single most likely explanation for the lack of bands on the final gel is a failure in the transformation of E. coli . When examined in conjunction with other plates of LBampicillin grown with the same aliquot of ampicillin, the ampicillin sample was found to be partially degraded. As a result, the working concentration of ampicillin in the LBampicillin plates was functionally too low, resulting in a lack of selective pressure and growth of nontransformed E. coli that contained no extrachromosomal plasmid. This led directly to a lack of isolated DNA from the MiniPrep. Thus, the bacterial chromosomal DNA was purified instead and was digested by the restriction enzymes at indiscriminate locations, yielding the entire range of DNA length. This resulted in a smear appearing on the gel rather [812]
than discrete bands. In the case of the supposed undigested sample, shearing of DNA from pipetting likely broke the chromosomal plasmid as well, resulting in the same smeared pattern. Columns six and eight contained slightly less visible smears than the other columns. This development can be attributed to potentially smaller volumes of digested DNA, either as a result of random selection of bacterial colonies with less plasmid DNA or the loss of DNA in the process of isolation. Another possibility lay in the actual pipetting of the DNA itself. As the pipette was depressed, some DNA may have escaped from the well into the buffer solution surrounding it, preventing the full volume of bacterial DNA from undergoing the electrophoresis process. Ultimately, the goal of the project was not accomplished, as the second gel electrophoresis analysis of eluted DNA resulted in a lack of bands appearing, indicating that elution of DNA was unsuccessful. All the same, given the success of all steps prior to the failed transformation of E. coli , it is exceedingly likely that repeating the same protocols with a new aliquot of ampicillin would result in the expected bands appearing on the final gel. CONCLUSION Had the ampicillin not degraded, the cloning of the eEF3 gene would have likely been successful. However, the possibility that the plasmid was not present in the bacteria cannot be ruled out since the final results merely confirmed that the colony chosen for the gel did not have the plasmid. Therefore, it can only be determined that the E. coli colony used for gel electrophoresis did not contain the recombinant plasmid due to the fact that degraded ampicillin was used on the plates, so there was no selection for ampicillinresistant bacteria to grow. In future studies, if fully functional ampicillin were to be used and the eEF3 gene were to be successfully transformed into E. coli with confirmation via gel electrophoresis, further research could be conducted to investigate the potential functional conservation of eEF3 in lower eukaryotic organisms. This could be explored by transforming the P. infestans plasmid that contains eEF3 into budding yeast, or S. cerevisiae , and applying selective pressures to promote the survival of budding yeast that take up the P. infestans eEF3containing plasmid and eject its own through the process of plasmid shuffling (Fig. 8). In order to determine if the transformation was successful and if the P. infestans eEF3 could functionally replace the S. cerevisiae eEF3, auxotrophic markers could be integrated into the recombinant plasmid. One such marker, leucine, is an amino acid commonly used in studies dealing with S. cerevisiae . LEU2 is a gene useful in encoding the enzymatic pathways necessary for leucine synthesis (16). In growth media lacking leucine, cells lacking the recombinant plasmid with a gene encoding for LEU2 would be unable to survive. Since the original S. cerevisiae plasmid does not contain the leucine marker while the recombinant plasmid from P. infestans does, this would select for the growth of budding yeast cells that took up the recombinant plasmid. [813]
Furthermore, the S. cerevisiae plasmid would contain a copy of the the URA3 gene. As another way to use such auxotrophic markers to place selective pressure on the yeast, S. cerevisiae could be placed on growth plates covered in 5fluoroorotic acid, or 5FOA. 5FOA is a fluorinated derivative of pyrimidine orotic acid used to select for the absence of the URA3 gene. The URA3 gene codes for an enzyme that will convert 5fluoroorotic acid into a toxic compound that induces apoptosis, thus urging the yeast to expunge its own DNA and accept the introduced plasmid (17). Figure 8. Plasmid shuffle schematic. Visual demonstration of insertion of recombinant DNA into yeast on 5FOA and the subsequent ejection of the original S. cerevisiae plasmid. WT eEF3 is the normal S. cerevisiae gene, PI eEF3 is the transfected P. infestans gene, and AMP is the ampicillin resistance gene (12). Currently, most medications for treating invasive fungal infections are either quite ineffective or hazardous to the health of the patient due to numerous negative side effects including host toxicity and antibiotic resistance, meaning that a new form of treatment is critical. If the functional conservation of eEF3 in lower eukaryotic organisms was confirmed in future studies through methods such as that detailed above, those results would render eEF3 an ideal drug target to combat detrimental diseases like potato blight and other fungal or similar pathogens. Such a universal antifungal drug would prove instrumental in efforts to control the outbreaks of most invasive fungal infections, both saving many human lives and protecting the integrity of global food supplies in the process. [814]
ACKNOWLEDGEMENTS We extend our sincerest gratitude and thanks to the following people and groups for their assistance in the completion of this project: Dr. Stephen Dunaway, Mitchell Dittus, Astré Bouchier, Justyna Pupek, New Jersey Governor’s School in the Sciences, Drew University, AT&T, Bayer Healthcare, Independent College Fund of New Jersey/Johnson & Johnson, The Overdeck Family Foundation, NJGSS Alumnae, Parents, and Corporate Matching Funds, The State of New Jersey, Board of Overseers of New Jersey Governor’s School in the Sciences The value of their help and mentorship throughout the process of this research endeavor cannot be understated. [815]
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