RpoS-dependent promoters require guanosine tetraphosphate for induction even in the presence of high levels of σs

RpoS-dependent promoters require ppGpp for induction in the stationary phase. This has been thought to be a simple consequence of sigma(S) itself requiring ppGpp for its production. By using four model promoters requiring sigma(S) for normal induction in the stationary phase, we demonstrate that sigma(3)-dependent promoters require ppGpp even in the presence of high levels of sigma(S) produced ectopically. Similar to sigma(70)-dependent promoters under positive control by ppGpp, the requirement of sigma(S)-dependent promoters for this alarmone is bypassed by specific "stringent" mutations in the beta-subunit of RNA polymerase. The results suggest that stationary phase induction of both sigma(S)- and sigma(70)-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 alpha-factor.