Starvation-induced expression of SspA and SspB: the effects of a null mutation in sspA on Escherichia coli protein synthesis and survival during growth and prolonged starvation.

Maxicell labelling and two-dimensional gel electrophoresis (2-D PAGE) have identified the proteins encoded by sspA and sspB (SspA, SspB) as proteins D27.1 and A25.8, respectively, in the Escherichia coli gene-protein database. SspA expression increases with decreasing growth rate and is induced by glucose, nitrogen, phosphate or amino acid starvation. The promoter, Pssp, is similar to gearbox promoters. Inactivation of SspA (sspA::neo) blocks sspB expression. [35S]-methionine-labelled proteins synthesized during growth and during stationary phase are different in delta sspA strains compared to sspA+ strains. This difference is enhanced during extended stationary phase (24-72 h). Long-term (10 d) viability of arginine-starved isogenic strains shows that sspA+ cultures remain viable significantly longer than delta sspA mutants. 2-D PAGE of proteins expressed during exponential growth shows that expression of at least 11 proteins is altered in delta sspA strains. A functional relA gene is required for sspA to affect protein synthesis.