Abstract
In Escherichia coli DNA damage results in the induction of the SOS response pathway that leads to an increase in expression of the DNA repair proteins. Recently other DNA damage response pathways have been identified. There is evidence indicating that DnaA may function to regulate a RecA/LexA independent pathway. This study focuses on the expression and potential regulation of 20 genes in response to DNA damage caused by Azidothymidine. Luciferase reporter constructs were assayed in three different background E.coli strains to determine if the genes were involved in RecA/LexA dependent or independent DNA damage response pathway. This study reports an increase in expression of several components of Pol III holoenzyme (dnaQ, holE, dnaX, holA, holB, and holC) following DNA damage, and this expression is independent of the SOS pathway. Several of these subunits may be regulated by DnaA: ε (dnaQ), δ (holA), and δ’ (holB). Following DNA damage the expression of DNA Pol I is inconclusive, although it does appear to be independent of LexA cleavage. An increase in the expression of several components of the primosome complex (priA, priB, and dnaTC) occurs following DNA damage, and expression of these genes is independent of LexA cleavage. Regarding priA expression, it does appear to be regulated by DnaA. A subunit of RecFOR (recO) is expressed following DNA damage and this expression is independent of the SOS pathway and not regulated by DnaA. ssb expression does increase following DNA damage and is not regulated by LexA/RecA or DnaA. The results of this study show that expression of Gryase increases following DNA damage, and is also not regulated by LexA/RecA or DnaA. The expression of ligA is independent of the SOS response, but appears to be dependent on DnaA. In this study an increase in expression of upp is independent of LexA cleavage, it does appear that the DnaA may regulate upp expression. This work adds to the growing body of evidence that indicates DnaA also functions as a transcriptional regulator of several genes in response to DNA damage in E.coli. Beyond characterizing the mechanism of regulation by DnaA, these results should also be validated using other SOS inducible mechanisms of DNA damage.