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Identifying Genes in E. coli Required for Susceptibility to Antisense Antibiotics Susan Puckett Mentor: Dr. Bruce Geller AVI BioPharma Howard Hughes Medical Institute
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Antibiotics Today Race against antibiotic resistance MRSA MDR & XDR Tuberculosis According to the CDC, “more than 70% of the bacteria that cause hospital-acquired infections are resistant to at least one of the drugs most commonly used to treat them.” (http://www.cdc.gov/ncidod/dhqp/ar.html)
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DNA mimics as antibiotics Phosphorodiamidate morpholino oligomers (PMOs) Antisense mechanism Disrupts protein synthesis (translation) by blocking ribosome Man-made, can be targeted GTGATAGCTTC AUGAGCACUAUCGAAGA RNA PMO http://www.stat.stanford.edu/~susan/courses /s166/node2.html
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Getting PMOs into the cell Naked PMO ineffective Cationic peptides Mechanism of PMO entry unknown Last year work: Found mutants resistant to peptide-PMOs Resistance was linked to peptide and not to PMO PMO peptide
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Questions What happens to the PMO once it gets into the cell? broken down? How does the PMO get in? transporter? Mutants: what is mutating? Are there genes that code for proteins necessary for the PMOs to be effective? What are these genes?
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Escherichia coli strain AS19 E. coli lab strains good for experiments AS19: permeable outer membrane Naked PMOs (without peptides) can get in http://www.conceptdraw.com/en/sampletour/medical/ Gram-Negative Envelope
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AS19 mutations AS19 was plated on agar plate containing enough naked PMO to prevent growth However, after 24 hour incubation there were several colonies growing
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AS19 mutant testing Vancomycin Revertant test antibiotic. Picked 10 mutants that were susceptible. Rifampin, erythromycin 100 x Resistant to AcpP PMO Mutants also resistant to FtsZ and GyrA PMOs
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Library Experiment Making competent cells of mutants and introducing an E. coli library Library: plasmids containing different pieces of the genome One plasmid per competent cell Hypothesis: one plasmid will contain gene that has mutated and that this gene will cause the PMO to once again become effective After 40 plate sets, no susceptible strains found
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Conclusions AS19 mutants resistant to naked AcpP PMO have been found Mutants picked are not revertants back to the non-leaky E. coli strain Mutations have not been in the target region of the PMO Library experiment did not result in finding any susceptible strains
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Gene Knockout Experiment with W3110 Use phage to insert transposon to knock out gene Hypothesis: A gene or genes is (are) necessary for PMO efficacy & can be knocked out to produce a PMO- resistant phenotype Lambda phage http://www.steve.gb.com/science/model_organisms.html
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Gene Knockout Steps Insert Tn5 transposon randomly in W3110 genome through phage infection Plate on kanamycin/(RFF)3R-AcpP PMO Purify DNA from colony of interest Digest genomic DNA and pUC19 DNA with KpnI, ligate Use competent cells, plate on kanamycin KpnI
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Results 2 colonies, named pUCTn5-1 and pUCTn5-2 Purify plasmid DNA, select primers that would surround insert Sequence into insert about 500 nucleotides BLAST search comparing to W3110 genome http://www.ncbi.nlm.nih.gov/sites/entrez?db=genomeprj&cmd=Retrieve&dopt=Overview&list_uids=16351 Tn5 insert was found to be here
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Conclusions AS19 was more difficult to experiment with despite the PMOs not needing peptides and gene for PMO susceptibility was not identified Gene knockout experiment: one gene necessary for the (RFF)3R-AcpP PMO to be effective is or is near the yehL gene in the E. coli W3110 genome
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What does this mean? Gene function in region might suggest mechanism of susceptibility This could show how the PMO is getting into the cell, how the PMO is degraded, or other mechanisms to inactivate the PMO Peptide-PMOs could then be designed with this new knowledge in mind
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Acknowledgements Howard Hughes Medical Institute URISC AVI BioPharma Oregon State University Dr. Kevin Ahern Dr. Bruce Geller Brett Mellbye Georgi Mitev
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