Regulation of the Cold Shock Response

In contrast to the heat shock response, there is only limited information on the regulation of the cold shock response, and this exists only for E. coli. Most publications deal with the regulatory role of CspA after a temperature downshock. 

What could be the signal for the induction of the cold shock proteins It has been observed that shifting E. coli cells from 37 to 5 °C results in an accumulation of 70S monosomes with a concomitant decrease in the number of polysomes [129]. Further, it has been shown that a cold shock response is induced when ribosomal function is inhibited, e.g. by cold-sensitive ribosomal mutations [121] or by certain antibiotics such as chloramphenicol [94]. These data indicate that the physiological signal for the induction of the cold shock response is inhibition of translation caused by the abrupt shift to lower temperature. Then, the cold shock proteins RbfA, CsdA and IF2 associate with the 70S ribosomes to convert the cold-sensitive nontranslatable ribosomes into cold-resistant translatable ribosomes. This in turn results in an increase in cellular protein synthesis and growth of the cells. 

In contrast to most mRNAs, which become untranslatable after a temperature downshock, cold shock mRNAs possess a mechanism to form the translation initiation complex at low temperature without cold shock ribosomes. A close inspection of the mRNAs of class I cold shock proteins reveal that they are equipped with an extra ribosome-binding site called the downstream box located within the coding region of their transcript [130]. It would be interesting to know whether introduction of this downstream box into a cellular mRNA would convert it into a transcript which can be transcribed immediately after a cold shock. In the case of the cspA mRNA it has been shown that in the absence of the downstream box the initiation complex cannot be formed at low temperature during the accHmation phase [131]. 

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