In order to analyse the mechanism of cold shock induction of CspA, a major cold shock protein of Escherichia coli, deletion analysis of the cspA gene was carried out. It was found that (i) the AT-rich sequence (-47 to -38) upstream of the cspA -35 region may act as the UP element playing a crucial role in cspA transcription at both 37 degrees C and 15 degrees C; (ii) the unusually long 5'-UTR of the cspA mRNA has negative effects on cspA expression at 37 degrees C; and (iii) in contrast, the 5'-UTR exerts a positive effect on mRNA stabilization at low temperature. Furthermore, it was demonstrated that the 14 base downstream box (DB) locating 12 bases downstream of the initiation codon of the cspA mRNA and complementary to a region near the decoding region of 16S rRNA was essential for the mRNA translation during the growth lag acclimation phase immediately after cold shock. During this phase, translation of non-cold shock gene mRNAs is blocked, since they require cold shock-specific ribosomal factors for the formation of the translation initiation complex. It is proposed that DB in cold shock mRNAs allows the formation of a stable initiation complex at low temperature in the absence of the cold shock ribosomal factors.