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

RpoS-dependent promoters require ppGpp for induction in the stationary phase. This has been thought to be a simple consequence of final sigma(S) itself requiring ppGpp for its production. By using four model promoters requiring final sigma(S) for normal induction in the stationary phase, we demonstrate that final sigma(S)-dependent promoters require ppGpp even in the presence of high levels of final sigma(S) produced ectopically. Similar to final sigma(70)-dependent promoters under positive control by ppGpp, the requirement of final 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 final sigma(S)- and final 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 final sigma-factor.