THE ROLE OF THE 5'-END UNTRANSLATED REGION OF THE MESSENGER-RNA FOR CSPA, THE MAJOR COLD-SHOCK PROTEIN OF ESCHERICHIA-COLI, IN COLD-SHOCK ADAPTATION

During cellular adaptation to low temperature, Escherichia coli transi ently synthesizes the major cold-shock protein CspA. It was found that adapation to cold shock is blocked when the 143-base sequence of the 5' untranslated region (5' 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 prote ins and cell growth was observed. Interestingly, when CspA was also ov erproduced together with the 5' UTR, normal cold-shock adaptive respon se was resumed without a prolonged lag period of cell growth. This ind icates that the 5' UTR of the cspA mRNA and its gene product CspA play a critical role in the regulation of the expression of cold-shock gen es and cold-shock adaptation. An 11-base common sequence (cold box) wa s found in the 5' UTRs of cspA, cspB, and csdA mRNAs. Indeed, the 25-b ase sequence within the 5' UTR of the cspA mRNA containing the cold-bo x sequence was able to prolong CspA production at 15 degrees C. We pro pose that a putative repressor binds to the cold-box sequence of the c old-shock mRNAs during the adaptive process and this binding in turn b locks the transcription of the cold-shock genes or destablilizes their mRNAs. CspA appears to promote either directly or indirectly the repr essor function.