ROLE OF THE COLD-BOX REGION IN THE 5' UNTRANSLATED REGION OF THE CSPAMESSENGER-RNA IN ITS TRANSIENT EXPRESSION AT LOW-TEMPERATURE IN ESCHERICHIA-COLI

Upon temperature downshift, a group of proteins sailed cold shock prot eins, such as CspA, CspB, and CsdA, are transiently induced in Escheri chia coli. However, when the 5' untranslated region (5' UTR) of cspA m RNA is overproduced at low temperature, the expression of cold shock g enes is prolonged or derepressed. It has been proposed that this effec t is due to highly conserved Il base sequences designated the ''cold b ox'' existing in the 5' UTRs of cspA, cspB, and csdA. Here, we demonst rate that the overproduction of the 5' UTR of not only cspA but also c spB and csdA mRNAs causes derepression of all three genes at the same Lime, Conversely, when the cold-box region was deleted from the cspA 5 ' UTR its derepression function was abolished, The amount of mRNA from the chromosomal cspA gene was much higher in cells overproducing the wild-type 5' UTR by means of a plasmid than it was In cells overproduc ing the cold-box-deleted 5' UTR. The stability of the chromosomal cspA mRNA in cells overproducing the wild-type 5' UTR was almost identical to that in cells overproducing the cold-box-deleted 5' UTR, Therefore , the derepression of cspA caused by overproduction of 5' UTR al the e nd of the acclimation phase occurs at the level of transcription but n ot bg mRNA stabilization, indicating that the cold-box region plays a negative role in cspA transcription in cold shock-adapted cells, The r ole of the cold-box region was further confirmed with a cspA mutant st rain containing a cold-hox-deleted cspA gene integrated into the chrom osome, which showed a high level of constitutive production of CspA bu t not CspB during exponential growth at low temperature.