Structure in solution of the major cold-shock protein from Bacillus subtilis

Abstract

THE cold-shock domain (CSD) is found in many eukaryotic transcriptional factors and is responsible for the specific binding to DNA of a cis-element called the Y-box^1–3. The same domain exists in the sequence of the Xenopus RNA-binding proteins FRG Y₁, and FRG Y₂ (refs 1, 3). The major cold-shock proteins of Escherichia coli (CS7.4)^4–7 and B. subtilis (CspB)⁸ have sequences that are more than 40 per cent identical to the cold-shock domain. We present here the three-dimensional structure of CspB determined by nuclear magnetic resonance spectroscopy. The 67-residue protein consists of an antiparallel five-stranded β-barrel with strands connected by turns and loops. The structure resembles that of staphylococcal nuclease and the gene-5 single-stranded-DNA-binding protein^9–11. A three-stranded β-sheet, which contains the conserved RNA-binding motif RNP1 as well as a motif similar to RNP2 in two neighbouring antiparallel β-strands^12–14, has basic and aromatic residues at its surface which could serve as a binding site for single-stranded DNA. CspB binds to single-stranded DNA in gel retardation experiments.