Almost all drug resistance in Mycobacterium tuberculosis (Mtb) results from single nucleotide polymorphisms. When left alone, the Mtb genome has a low mutation frequency compared to other microorganisms. During drug treatment, however, mutation is much more common. RecA is a protein used to repair a sequence of damaged DNA by copying in a similar sequence from elsewhere in the genome. If the repair is not a perfect match, the RecA has been observed to release after it repairs if a thermostable mismatch is present, but will ideally remain attached to the sequence if a perfect match is not found. In Mtb there is no mismatch repair mechanism, meaning that after RecA releases the sequence from repair, there is no proofreader mechanism to replace an incorrect match. To investigate the potential of RecA involvement in drug resistant mutation events, relative binding strength of RecA to specific Mtb short sequence triplets (83-mer single stranded oligonucleotides of triplicated 27 nucleotide sequences) was evaluated using electrophoretic mobility shift assays (EMSA’s) at or near the S315 codon on the katG gene and the S450 codon on the rpoß gene. Mutation at these locations imparts isoniazid and rifampin resistance respectively. Particularly on the SST’s that include the codon of interest, weak binding observed suggests that RecA is highly tolerant of mismatches at the drug resistant mutation sites.

Implications of RecA binding in Mycobacterium tuberculosis

2019 Spring National Meeting

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