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

S. A. Goff, L. P. Casson, A. L. Goldberg

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Abstract

Upon a shift to high temperature, Escherichia 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°C and fail to respond to a shift to 42°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 on double mutants. The activity of protease La was higher in wild-type cells than in htpR mutants grown at 30°C and increased upon shift to 42°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°C and 37° 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 2-3 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.

Original languageEnglish (US)
Pages (from-to)6647-6651
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume81
Issue number21 I
DOIs
StatePublished - Jan 1 1984

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