Treatment with DNA-damaging agents increases expression of polA'-'lacZ gene fusions in Escherichia coli K-12.

The polA gene of Escherichia coli encodes the DNA polymerase I that is involved in DNA replication and repair. In contrast to the extensive body of data on the structure and function of polymerase I, there is little information available concerning the mechanisms that govern polA expression. Here, we studied the expression of the polA gene using translational fusions to lacZ. We found that treatment with the DNA-damaging agents 4-nitroquinoline-N-oxide (4-NQO), UV light mitomycin C (MC) and methyl methanesulfonate (MMS) leads to enhanced expression of polA'-'lacZ fusions. The increase in expression of polA reflects stimulation of transcription from a single promoter, as determined by S1 nuclease analyses. This was not observed in mutants that are blocked in induction of the SOS regulon. However, mutants with defective excision repair were more susceptible to polA stimulation. These results support the hypothesis that increased polA expression may be important for the ability to repair bulky DNA adducts that interfere with replication.