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 electro-phoresis (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, P_ssp, 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 δsspA 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 δsspA mutants. 2-D PAGE of proteins expressed during exponential growth shows that expression of at least 11 proteins is altered in δsspA strains. A functional relA gene is required for sspA to affect protein synthesis.