6S RNA function enhances long-term cell survival.

6S RNA was identified in Escherichia coli >30 years ago, but the physiological role of this RNA has remained elusive. Here, we demonstrate that 6S RNA-deficient cells are at a disadvantage for survival in stationary phase, a time when 6S RNA regulates transcription. Growth defects were most apparent as a decrease in the competitive fitness of cells lacking 6S RNA. To decipher the molecular mechanisms underlying the growth defects, we have expanded studies of 6S RNA effects on transcription. 6S RNA inhibition of sigma(70)-dependent transcription was not ubiquitous, in spite of the fact that the vast majority of sigma(70)-RNA polymerase is bound by 6S RNA during stationary phase. The sigma(70)-dependent promoters inhibited by 6S RNA contain an extended -10 promoter element, suggesting that this feature may define a class of 6S RNA-regulated genes. We also discovered a secondary effect of 6S RNA in the activation of sigma(S)-dependent transcription at several promoters. We conclude that 6S RNA regulation of both sigma(70) and sigma(S) activities contributes to increased cell persistence during nutrient deprivation.