Jiang W, Fang L, Inouye M
Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway 08854, USA.
J Bacteriol. 1996 Aug;178(16):4919-25. doi: 10.1128/jb.178.16.4919-4925.1996.
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 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 proteins and cell growth was observed. Interestingly, when CspA was also overproduced together with the 5' UTR, normal cold-shock adaptive response was resumed without a prolonged lag period of cell growth. This indicates 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 genes and cold-shock adaptation. An 11-base common sequence (cold box) was found in the 5' UTRs of cspA, cspB, and csdA mRNAs. Indeed, the 25-base sequence within the 5' 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.
在细胞适应低温的过程中，大肠杆菌会短暂合成主要的冷休克蛋白CspA。研究发现，当cspA mRNA的5'非翻译区（5'UTR）的143个碱基序列过量产生时，冷休克适应过程会被阻断。在15摄氏度下过量产生该UTR不仅导致CspA的合成不再短暂，而且使其他冷休克蛋白如CspB和CsdA的合成延长。此外，还观察到冷休克蛋白以外的细胞蛋白合成及细胞生长受到抑制。有趣的是，当CspA与5'UTR一起过量产生时，正常的冷休克适应性反应得以恢复，且细胞生长没有延长的延迟期。这表明cspA mRNA的5'UTR及其基因产物CspA在冷休克基因表达调控和冷休克适应中起关键作用。在cspA、cspB和csdA mRNA的5'UTR中发现了一个11个碱基的共有序列（冷框）。实际上，cspA mRNA的5'UTR内包含冷框序列的25个碱基序列能够在15摄氏度下延长CspA的产生。我们推测在适应过程中，一种假定的阻遏物与冷休克mRNA的冷框序列结合，这种结合反过来会阻断冷休克基因的转录或使其mRNA不稳定。CspA似乎直接或间接促进了阻遏物的功能。
