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Cold shock genes cspA and cspB from Caulobacter crescentus are post-transcriptionally regulated and important for cold adaptation


Cold shock proteins (CSPs) are nucleic acid binding chaperones, first described as being induced to solve the problem of mRNA stabilization after temperature downshift. C. crescentus has four CSPs, being CspA and CspB cold-induced, while CspC and CspD are induced only in stationary phase. In this work we have determined that the synthesis of both CspA and CspB reaches the maximum levels early in the acclimation phase. The deletion of cspA causes a decrease in growth at low temperature whereas the cspB strain has a very subtle and transient cold-related growth phenotype. The double mutant cspA/cspB has a slightly more severe phenotype than that of the cspA mutant, suggesting that, although CspA may be more important to cold adaptation than CspB, both proteins have a role in this process. Gene expression analyses were carried out using cspA and cspB regulatory fusions to the lacZ reporter gene, and showed that both genes are regulated at the transcriptional and post-transcriptional levels. Deletion mapping of the long 5'-UTR of each gene identified a common region important for cold induction, probably via translation enhancement. Differently from what was reported for other bacteria, these cold shock genes have no regulatory regions downstream from ATG that are important for cold induction. This work shows that the importance of CspA and CspB to C. crescentus cold adaptation, mechanisms of regulation and pattern of expression during acclimation phase apparently differ in many aspects from what was described so far for other bacteria. (AU)

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