Differential thermoregulation of two highly homologous cold-shock genes, cspA and cspB, of Escherichia coli

Background: The major cold-shock protein in Escherichia coli is CspA, a 7.4 kDa protein. A CspA family has been found which consists of four additional proteins, CspB, CspC, CspD and CspE. The expression of cspB, unlike the other homologues, is cold-shock inducible like cspA. Results: We examined the cold-shock induction of CspA and CspB at various temperatures, The cspA induction is observed by temperature shift from 37 to 30 degrees C and high levels of CspA production are observed between 24 and 10 degrees C. In contrast, CspB production occurs only by temperature shift to below 20 degrees C, with maximum induction at 15 degrees C. Both cspA and cspB expressions were found to be induced at the level of transcription as determined by primer extension. Conclusions: These results show that cspA and cspB expressions are differentially regulated at low temperature indicating that E. coli contains at least two different biothermostats or thermoregulators that are likely to play important roles in cellular adaptation to low temperature. The cspB promoter shows sequence similarity to the cspA promoter. Furthermore, both cspA and cspB mRNAs have unusually long 5' untranslated regions (159 and 161 bases, respectively), both of which are able to form similar extensive secondary structures. These features are considered to contribute to the nature of the thermostats for cspA and cspB.