The Cold Shock Response

Very recently, a third hypothesis has been pubHshed. Morita and co-workers [47] have suggested that the rpoH mRNA secondary structure itself acts as a thermosensor. In the absence of heat stress, the rpoH mRNA is folded into a secondary structure that occludes the ribosome binding site and the initiation codon. Upon heat shock, this structure is unfolded allowing ribosome binding and enhanced synthesis. 

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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. 

It has been suggested that the ribosome might act as the sensor for the cold shock response [94,99], and it was postulated that the physiological signal for the induction of the cold shock response may be inhibition of initiation of... 

RNA thermosensors that turn on gene expression in response to cold shock have also been observed." In systems of this type, the RNA element that forms at low temperature is predicted to compete with a structure that would otherwise inhibit expression, so that a shift to a lower growth temperature results in induction of the cold-shock response. These systems are less well characterized than the heat-responsive thermosensor RNAs. 

Beckering, C.L., Steil, L., Weber, M.H., Volker, U. and Marahiel, M.A. Genomewide transcriptional analysis of the cold shock response in Bacillus s-ubtilis. J Bacterial, 184 (2002) 6395-6402. 

Both the heat and cold shock response are universal and have been studied extensively. The major heat shock proteins (HSPs) are highly conserved. They are involved in the homeostatic adaptation of cells to harsh environmental conditions. Some act as molecular chaperones for protein folding, while others are involved in the processing of denatured polypeptides whose accumulation would be deleterious. The cold shock results in the transient induction of cold shock proteins (CSPs), which include a family of small acidic proteins carrying the cold shock domain. The CSPs appear to be involved in various cellular functions such as transcription, translation and DNA recombination. 

A second example of an apparent absence of the heat-shock response was found in studies of cold-adapted, stenothermal Antarctic notothe-nioid fishes that never encounter temperatures above 0°C and die of heat death above 4°C... 

Liu, A.Y.C, H.J. Bian, L.E. Huang, and Y.K. Lee (1994). Transient cold-shock induces the heat-shock response upon recovery at 37 degrees C in human cells. J. Biol. Chem. 269 14768-14775. 

A group of proteins that are synthesized by plant cells, prokaryotic cells, and eukaryotic cells in response to cold stress. It has been suggested that cold-shock proteins (CSPs) function as chaperones for mRNA. See Graumann, P.L. and Marshiel, M. A., A superfamily of proteins that contain the cold-shock domain, Trends Biochem. Sci. 23,286-290,1998 Phadtare,... 

Klein, W., Weber, M.H. and Marahiel, M.A. Cold shock response of Bacillus subtilis isoleucine-dependent switch in the fatty acid branching pattern for membrane adaptation to low temperatures. JBacterial, 181 (1999) 5341-5349. 

Lee, K. (2004). Cold shock response in Lactococcus lactis subsp. diacetylactis a comparison of the protection generated by brief pre-treatment at less severe temperatures. Process Biochemistry, 39(12), 2233-2239. 

Watson, P.F. Plummer, J.M. (1985). The responses of boar sperm membranes to cold shock and cooling. In Deep Freezing of Boar Semen (Johnson, L.A. Larsson, K., eds.), pp. 113-128, Swedish University of Agricultural Sciences, Uppsala, Sweden. 

Besides HS, selective plant Hsps are induced in response to different abiotic stresses such as heavy-metal stress, water stress, wounding stress, salt stress, cold shock, and anoxia stress. Plants, in general, survive lethal temperature stress more efficiently after prior exposure to a mild stress as against a direct response to lethal stress. This phenomenon is termed acquired thermotolerance [103]. Hsp are believed to be important for the protection of cells against heat injury both in basal thermotolerance (i.e., thermotolerance shown without prior heat shock) as well as in acquired thermotolerance responses. 

Al-Fageeh, M.B. and Smales, C.M. Control and regulation of the cellular responses to cold shock the responses in yeast and mammalian systems. Biachem J, 397(2006) 247-259. 

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