UNIVERSAL NUCLEIC ACID-BINDING DOMAIN REVEALED BY CRYSTAL-STRUCTURE OF THE BACILLUS-SUBTILIS MAJOR COLD-SHOCK PROTEIN

THE cold-shock response in both Escherichia coli and Bacillus subtilis is induced by an abrupt downshift in growth temperature. It leads to the increased production of the major cold-shock proteins, CS7.4 and CspB, respectively1-3. CS7.4 is a transcriptional activator of two genes4,5. CS7.4 and CspB share 43 per cent sequence identity with the nucleic acid-binding domain of the eukaryotic gene-regulatory Y-box factors6. This cold-shock domain is conserved from bacteria to man7 and contains the RNA-binding RNP1 sequence motif8. As a prototype of the cold-shock domain, the structure of CspB has been determined here from two crystal forms. In both, CspB is present as an antiparallel five-stranded beta-barrel. Three consecutive beta-strands, the central one containing the RNP1 motif, create a surface rich in aromatic and basic residues that are presumably involved in nucleic acid binding. Preferential binding of CspB to single-stranded DNA is observed in gel retardation experiments.