Escherichia coli CspA-family RNA chaperones are transcription antiterminators

CspA, the major cold-shock protein of Escherichia coli, is an RNA chaperone, which is thought to facilitate translation at low temperature by destabilizing mRNA structures. Here we demonstrate that CspA, as well as homologous RNA chaperones CspE and CspC, are transcription antiterminators. In vitro, the addition of physiological concentrations of recombinant CspA, CspE, or CspC decreased transcription termination at several intrinsic terminators and also decreased transcription pausing. In vivo, overexpression of cloned CspC and CspE at 37°C was sufficient to induce transcription of the metY-rpsO operon genes nusA, infB, rbfA, and pnp located downstream of multiple transcription terminators. Similar induction of downstream metY-rpsO operon genes was observed at cold shock, a condition to which the cell responds by massive overproduction of CspA. The products of nusA, infB, rbfA, and pnp—NusA, IF2, RbfA, and PNP—are known to be induced at cold shock. We propose that the cold-shock induction of nusA, infB, rbfA, and pnp occurs through transcription antitermination, which is mediated by CspA and other cold shock-induced Csp proteins.