Stringent starvation protein A (ssPA), a member of the GST superfamily, is an RNA polymerase-associated transcriptional activator for the lytic development of phage P1 and is essential for stationary phase-induced acid tolerance of E. coli. It indicates that the flexible regions are not critical for SspA function, whereas the surface pocket is important for both transcriptional activation of the phage P1 late promoter and acid resistance of E. coli. SspA is known to be implicated in survival during nutrient starvation and prolonged stationary phase. Recently, SspA was shown to play an important role in the stationary phase-induced stress response including acid tolerance by down-regulating the level of the global regulator H-NS, which negatively regulates multiple stress defense systems.