The role of the 5'-end untranslated region of the mRNA for CspA, the major cold-shock protein of Escherichia coli, in cold-shock adaptation

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Abstract
During cellular adaptation to low temperature, Escherichia coli transiently synthesizes the major cold-shock protein CspA. It was found that adaptation to cold shock is blocked when the 143-base sequence of the 59 untranslated region (59 UTR) of the cspA mRNA is overproduced. The overproduction of this UTR at 15 degrees C caused the synthesis of not only CspA but also other cold-shock proteins such as CspB and CsdA to be no longer transient but rather prolonged. In addition, inhibition of both the synthesis of cellular proteins other than cold-shock proteins and cell growth was observed. Interestingly, when CspA was also overproduced together with the 59 UTR, normal cold-shock adaptive response was resumed without a prolonged lag period of cell growth. This indicates that the 59 UTR of the cspA mRNA and its gene product CspA play a critical role in the regulation of the expression of cold-shock genes and cold-shock adaptation. An 11-base common sequence (cold box) was found in the 59 UTRs of cspA, cspB, and csdA mRNAs. Indeed, the 25-base sequence within the 59 UTR of the cspA mRNA containing the cold-box sequence was able to prolong CspA production at 15 degrees C. We propose that a putative repressor binds to the cold-box sequence of the cold-shock mRNAs during the adaptive process and this binding in turn blocks the transcription of the cold-shock genes or destabilizes their mRNAs. CspA appears to promote either directly or indirectly the repressor function.