CSPA, THE MAJOR COLD-SHOCK PROTEIN OF ESCHERICHIA-COLI, IS AN RNA CHAPERONE

CspA, the major cold-shock protein of Escherichia coli, is dramaticall y induced during the cold-shock response, The amino acid sequence of C spA shows 43% identity to the ''cold-shock domain'' of the eukaryotic Y-box protein family, which interacts with RNA and DNA to regulate the ir functions, Here, we demonstrate that CspA binds to RNA as a chapero ne, First, CspA cooperatively binds to heat-denatured single stranded RNA if it is larger than 74 bases, causing a supershift in gel electro phoresis. A minimal concentration of CspA at 2.7 x 10(-5) M is absolut ely required for this cooperative binding, which is sufficiently lower than the estimated cellular concentration of CspA (10(-4) M) in cold shocked cells, No specific RNA sequences for CspA binding were identif ied, indicating that it has a broad sequence specificity for its bindi ng, When the 142-base 5'-untranslated region of the cspA mRNA was used as a substrate for ribonucleases A and T1, the addition of CspA signi ficantly stimulated RNA hydrolysis by preventing the formation of RNas e-resistant bands due to stable secondary structures in the 5'-untrans lated region, These results indicate that binding of CspA to RNA desta bilizes RNA secondary structures to make them susceptible to ribonucle ases, We propose that CspA functions as an RNA chaperone to prevent th e formation of secondary structures in RNA molecules at low temperatur e, Such a function may be crucial for efficient translation of mRNAs a t low temperatures and may also have an effect on transcription.