Cold shock genes CspA and CspB from caulobacter crescentus are post transcriptionally regulated and important for cold adaptation

Abstract

Cold shock proteins (CSPs) are nucleic acid binding chaperones, first described as being induced to solve the problem of mRNA stabilization after temperature downshift. Caulobacter crescentus has four CSPs: CspA and CspB, which are cold induced, andCspC and CspD, which are induced only in stationary phase. In this work we have determined that the synthesis of both CspAand CspB reaches the maximum levels early in the acclimation phase. The deletion of cspA causes a decrease in growth at lowtemperature, whereas the strain with a deletion of cspB has a very subtle and transient cold-related growth phenotype. The cspAcspB double mutant has a slightly more severe phenotype than that of the cspA mutant, suggesting that although CspA maybemore important to cold adaptation than CspB, both proteins have a role in this process. Gene expression analyses were carriedout using cspA and cspB regulatory fusions to the lacZ reporter gene and showed that both genes are regulated at the transcriptional and posttranscriptional levels. Deletion mapping of the long 5=-untranslated region (5=-UTR) of each gene identified acommon region important for cold induction, probably via translation enhancement. In contrast to what was reported for otherbacteria, these cold shock genes have no regulatory regions downstream from ATG that are important for cold induction. Thiswork shows that the importance of CspA and CspB to C. crescentus cold adaptation, mechanisms of regulation, and pattern ofexpression during the acclimation phase apparently differs in many aspects from what has been described so far for other bacteria. © 2012, American Society for Microbiology.