The SOS response is a cellular defense mechanism in bacteria, regulated by the LexA and RecA proteins. This response is directly related to bacterial mutagenesis and evolution. The mutagenic aspect of the SOS response is due to the presence of error-prone DNA polymerases. These enzymes help the cell to tolerate lesions in DNA by performing translesion synthesis (TLS), a process in which mutations can be introduced. In this work, we use Caulobacter crescentus as a model bacterium. It possesses the imuAB dnaE2 operon, which has a function analogous to the DNA polymerase V of E. coli. This operon is present in several bacterial genomes, but little is understood about its mechanism of action. Our main goals are to evaluate the untargeted mutagenesis (i. e. mutagenesis not directed to DNA damage sites) mediated by these genes, and to determine if the imuA protein has some role in SOS induction, given its similarity to RecA. We have constructed strain containing an operator constitutive version of the imuAB dnaE2 operon, and we will confirm the increased expression of these genes in this strain. Spontaneous mutation rates will be measured to determine the presence of untargeted SOS mutagenesis. To ascertain the role of ImuA in SOS induction, we will measure the levels of expression of SOS genes using promoter fusions with lacZ, both in wild-type and delta imuA strains.
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