Induction of CspA, an E. coli major cold‐shock protein, upon nutritional upshift at 37 °C

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Abstract
Background: The synthesis of CspA, the major cold‐shock protein of Escherichia coli, is dramatically induced upon cold shock. It was recently reported that there is massive presence of CspA under nonstress conditions, and it is thus claimed that CspA as the cold‐shock protein is a misnomer.Results: Here, we re‐examined and confirmed that CspA is induced upon culture dilution at 37 °C. However, its induction level is one‐sixth of the cold‐shock‐induced level, clearly indicating that the major stress that induces CspA is cold shock. It was further found that CspA induction can be achieved not only by culture dilution but also by the simple addition of nutrients, and that it was almost completely abolished in the presence of rifampicin or nalidixic acid. Nutritional upshift causes the induction of only CspA but not other cold‐shock‐inducible CspA homologues. The amount of cspA mRNA rapidly and transiently increased by culture dilution, but its stability was not significantly changed.Conclusions: These results suggest that CspA is a nutritional‐upshift stress protein as well as a cold‐shock stress protein, and that CspA induction following nutritional upshift may be due to transcriptional activation.