title: 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, 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 degrees C and fail to respond to a shift to 42 degrees 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 degrees C and increased upon shift to 42 degrees 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 degrees C and 37 degrees 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.
mesh_terms: D049069:ATP-Dependent Proteases; D000255:Adenosine Triphosphate / Q000494:pharmacology; D001426:Bacterial Proteins / Q000378:metabolism*; D004274:DNA, Recombinant; D010450:Endopeptidases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D005809:Genes, Regulator; D006360:Heat-Shock Proteins / Q000235:genetics*; D006358:Hot Temperature; D007763:Lac Operon; D009154:Mutation; D009876:Operon; D010641:Phenotype; D049070:Protease La; D012697:Serine Endopeptidases; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004274:DNA, Recombinant; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D000255:Adenosine Triphosphate; D001616:beta-Galactosidase; D010450:Endopeptidases; D049069:ATP-Dependent Proteases; D012697:Serine Endopeptidases; C483567:Lon protein, E coli; D049070:Protease La