Expression of thednaB gene ofEscherichia coli is inducible by replication-blocking DNA damage in arecA-independent manner Received: 4 April 1995
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- Kleinsteuber, S. & Quiñones, A. Molec. Gen. Genet. (1995) 248: 695. doi:10.1007/BF02191709
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The replicative DNA helicase encoded by thednaB gene is essential for chromosomal DNA replication inEscherichia coli. The DnaB protein is a component of the σX-type primosome which is regarded as a model system for lagging strand synthesis of the chromosome. Using translationallacZ fusions at the plasmid and chromosomal levels, we studied the influence of DNA-damaging agents ondnaB gene expression. We found that DNA damage caused by mitomycin C, methyl methanesulphonate, 4-nitroquinoline N-oxide, and UV irradiation led to a moderate, but significant induction ofdnaB gene expression. Comparative S1 analysis of transcripts in untreated and induced cells demonstrated that the induction is due to increased transcription from thednaB promoter. In contrast to other DNA damage-inducible replication genes, such asdnaA,dnaN,dnaQ, andpolA, expression of which is not inducible inrecA andlexA mutants, the induction ofdnaB was also observed in arecA1 mutant. These results show that the induction ofdnaB gene expression by replication-blocking DNA damage is due to a mechanism other than the indirectly SOS-dependent induction of the other DNA replication genes. Moreover, the data suggest that replication proteins are involved in recovery from replication-blocking DNA damage in two different ways — on the one hand at the level of initiation and on the other hand at the level of elongation.