6S RNA regulation of pspF transcription leads to altered cell survival at high pH.

6S RNA is a highly abundant small RNA that regulates transcription through direct interaction with RNA polymerase. Here we show that 6S RNA directly inhibits transcription of pspF, which subsequently leads to inhibition of pspABCDE and pspG expression. Cells without 6S RNA are able to survive at elevated pH better than wild-type cells due to loss of 6S RNA-regulation of pspF. This 6S RNA-dependent phenotype is eliminated in pspF-null cells, indicating that 6S RNA effects are conferred through PspF. Similar growth phenotypes are seen when PspF levels are increased in a 6S RNA-independent manner, signifying that changes to pspF expression are sufficient. Changes in survival at elevated pH most likely result from altered expression of pspABCDE and/or pspG, both of which require PspF for transcription and are indirectly regulated by 6S RNA. 6S RNA provides another layer of regulation in response to high pH during stationary phase. We propose that the normal role of 6S RNA at elevated pH is to limit the extent of the psp response under conditions of nutrient deprivation, perhaps facilitating appropriate allocation of diminishing resources.