Heat shock regulatory gene htpR influences rates of protein degradation and expression of the lon gene in Escherichia coli.

Abstract

Upon a shift to high temperature, E. coli increase their rate of protein degradation and also the expression of a set of heat shock genes. Nonsense mutants of htpR (also called hin), suppressed by a temperature-sensitive suppressor, show lower expression of heat shock genes at 30.degree. C and fail to respond to a shift to 42.degree. C. These mutants were found to have a lower capacity to degrade abnormal or incomplete proteins than that of wild-type cells. This reduction in proteolysis equals or exceeds that in lon mutants, which encode a defective ATP-dependent protease, protease La, and is particularly large in htpR lon double mutants. The activity of protease La was higher in wild-type cells than in htpR mutants grown at 30.degree. C and increased upon shift to 42.degree. C only in the wild type. To determine whether htpR influences transcription of the lon gene, a lon-lacZ operon fusion was utilized. Introduction of the htpR mutation reduced transcription from the lon promoter at 30.degree. C and 37.degree. C. This defect was corrected by a plasmid (pFN97) carrying the wild-type htpR allele. Induction of the heat shock response with ethanol had little or no effect in htpR mutants but stimulated lon transcription 2- to 3-fold in wild-type cells and htpR cells carrying pFN97. Thus, lon appears to be a heat shock gene, and increased synthesis of protease La under stressful conditions may help to prevent the accumulation of damaged cellular protein.