AN ANALOG OF THE DNAJ MOLECULAR CHAPERONE WHOSE EXPRESSION IS CONTROLLED BY A SIGMA(S) DURING THE STATIONARY-PHASE AND PHOSPHATE STARVATIONIN ESCHERICHIA-COLI

The Escherichia coil CbpA protein appears to be an analogue of the mol ecular chaperone, DnaJ, as judged from not only its structure but also its possible function. The expression of cbpA, however, was not signi ficantly affected by up-shift of the growth temperature. Remarkably, i t was found that the expression of cbpA was induced under certain grow th conditions, such as the entry of cells into stationary phase, or gr owth in a phosphate-limited medium. Such conditional expression of cbp A was regulated at the transcriptional level in a os-dependent manner. The structure of this os-dependent cbpA promoter was clarified by det ermining its transcription start site. The cbpA promoter region was fo und to contain an unusual DNA structure (i.e. DNA curvature). From the se results, it was suggested that, in contrast to DnaJ, CbpA may funct ion as a molecular chaperone in an adaptive response to environmental stresses other than heat shock.