EXPRESSION OF HEAT-SHOCK PROTEIN-D48.5 OF ESCHERICHIA-COLI IS SUBJECTTO MODULATION BY CATABOLITE REPRESSION

The Escherichia coli heat shock regulon consists of approximately twen ty polypeptides that are coordinately and transiently induced upon a t emperature upshift under the control of an alternative sigma factor, d esignated sigma-32 or HtpR. Preliminary observations on one of the pro teins of the heat shock response, protein D 48.5, suggested that its i nduction by sigma-32 during heat shock may be modulated by catabolite repression. In this study, a disk diffusion assay was used to screen t he effect of several compounds on the expression of a lacZ fusion in t he gene encoding protein D 48.5. This assay indicated that the express ion of this protein was controlled, at least in part, by the catabolit e repression response. A more indepth analysis of the expression of pr otein D 48.5 under both steady-state and heat shock conditions was con ducted in both a wild type and cya crp background. This analysis revea led that in the cya crp background, the steady-state level of protein D 48.5 was elevated relative to the wildtype, but that the heat shock induction of the protein was reduced in magnitude relative to the wild type strain, suggesting a direct link between these two global respon ses. The lacZ fusion in the structural gene for protein D 48.5 should prove useful as a reporter mechanism to probe the physiology and regul ation of the heat shock response.