Expression of the Escherichia coli dnaQ (mutD) gene is inducible

By promoter fusion to the galK gene and comparative S1 analysis we investigated the in vivo regulation of transcription of the dnaQ gene which encodes the epsilon-subunit of the DNA polymerase III holoenzyme carrying the 3'----5' exonucleolytic proofreading function. Induction of a mutagenic stress situation by treatment with the base analogue 2-aminopurine (2-AP) leads to an increase in dnaQ transcription. S1 mapping analysis of the two dnaQ transcripts revealed a differential promoter activation for this 2-AP induced increase in dnaQ transcription. In addition, a similar galK promoter fusion with the dnaN gene coding for the beta-subunit of the DNA polymerase III holoenzyme revealed that dnaN transcription is also 2-AP inducible as judged by galactokinase activity. This is the first evidence for the inducibility of dnaQ gene expression (and possibly of other genes of the DNA polymerase II holoenzyme) and is discussed in relation to DNA repair mechanisms.