The major cold shock protein of Bacillus subtilis, CspB, has been shown to affect the level of several cold-induced proteins in B. subtilis after cold shock. Here we show that the expression of CspB in Escherichia coli at 37 degrees C - conditions where the cold shock proteins CspA and CspB of E. coli are not present - resulted in a marked decrease in cellular growth rate and had a profound influence on the pattern of protein synthesis, as revealed by two-dimensional gel electrophoresis. This involves both decreases and increases in the rates of synthesis of specific proteins. Specifically, CspB induction resulted in enhanced beta-galactosidase activity expressed from a transcriptional hns-lacZ fusion. This increase reflects the induction of hns transcription and H-NS synthesis after cold shock, which has been demonstrated to be dependent on CspA in vitro. In contrast, expression of a mutant form of CspB (CspBF15A) that is unable to bind to ssDNA in vitro had no effect on growth rate, pattern of protein synthesis or beta-galactosidase activity. Our data demonstrate a strong influence of CspB on protein synthesis in E. coli and suggest a similar function for CspA in E. coli to that of CspB in B. subtilis.