RpoS-dependent promoters require guanosine tetraphosphate for induction even in the presence of high levels of σ(s)

Abstract

RpoS-dependent promoters require ppGpp for induction in the stationary phase. This has been thought to be a simple consequence of σ(s) itself requiring ppGpp for its production. By using four model promoters requiring σ(s) for normal induction in the stationary phase, we demonstrate that σ(s)-dependent promoters require ppGpp even in the presence of high levels of σ(s) produced ectopically. Similar to σ70-dependent promoters under positive control by ppGpp, the requirement of σ(s)-dependent promoters for this alarmone is bypassed by specific 'stringent' mutations in the β-subunit of RNA polymerase. The results suggest that stationary phase induction of both σ(s)- and σ70-dependent genes requires the stringent control modulon and that stringency confers dual control on the RpoS regulon by affecting promoter activity and the levels of the required σ-factor.