INDUCTION OF THE ESCHERICHIA-COLI AIDB GENE UNDER OXYGEN-LIMITING CONDITIONS REQUIRES A FUNCTIONAL RPOS (KATF) GENE

The Escherichia coli aidB gene is regulated by two different mechanism s, an ada dependent pathway triggered by methyl damage to DNA and an a da-independent pathway triggered when cells are grown without aeration . In this report we describe our search for mutations affecting the ad a-independent aidB induction pathway. The mutant strain identified car ries two mutations affecting aidB expression. These mutations are name d abrB (aidB regulator) and abrD. The abrB mutation is presently poorl y characterized because of instability of the phenotype it imparts. Th e second mutation, abrD1, reduces the expression of aidB observed when aeration is ceased and oxygen becomes limiting. Genetic and phenotypi c analysis of the abrD1 mutation demonstrates that it is an allele of rpoS. Thus, aidB is a member of the family of genes that are transcrib ed by a sigma(s)-directed RNA polymerase holoenzyme. Examination of ai dB expression in an rpoS insertion mutant strain indicates that both r poSl3::Tn10 and abrD1 mutations reduce aidB expression under oxygen-li miting conditions that prevail in unaerated cultures, reduce aidB indu ction by acetate at a low pH, but have little or no effect on the ada- dependent alkylation induction of aidB.