Heat shock regulatory gene (htpR) of Escherichia coli is required for growth at high temperature but is dispensable at low temperature.

Abstract

Nonsense mutations affecting the positive regulatory gene (htpR) of heat shock response have been obtained in a strain of Escherichia coli carrying no suppressor. The mutants can grow only at temperatures below 34°C-35°C. Heat, ethanol, and coumermycin induce major heat shock proteins in the wild-type but not in the htpR mutants. In contrast, the level of heat shock proteins synthesized at low temperature is unaffected. The htpR gene product is thus required for induction of heat shock proteins by heat or other stresses but not for their "basal-level" synthesis. Nucleotide sequence has been determined for the wild-type and the mutant alleles of htpR.The coding region appears to consist of 852 nucleotide pairs that correspond to 284 amino acids. Sequences commonly considered as signals for transcriptional initiation and termination were found flanking the coding region. Within this region, six amber, one opal, and two missense mutations were identified; the nonsense mutations are scattered along the gene, some being very close to the presumed amino terminus. These results indicate that the absence of htpR gene product is directly responsible for the failure to respond to heat shock or other stresses and for the inability to grow at high temperature. We propose that htpR represents a new class of genes that are essential for growth only at high temperatures (>35°C). Implications of the sequence homologies found among htpR, rpoD, and nusA proteins are discussed.A specific set of proteins called heat shock proteins (HSP) is induced when organisms or cells are exposed to high temperature or other environmental stresses. Such induction of HSP seems to represent part of homeostatic response, at the cellular level, to environmental changes in both eukaryotes and prokaryotes. Extensive structural homology between some of the HSP genes (1) and proteins (2) from a variety of distantly related organisms suggests that the response to heat shock or stress is universal and well conserved during evolution. In spite of the recent progress in this field, little is known about the mechanisms involved in regulating heatshock response.Induction of HSP in Escherichia coli occurs primarily at the transcriptional level (3, 4). Analysis of a mutant defective in heat shock induction led us to identify a gene (htpR or hin) whose product is apparently required for the enhanced transcription of heat shock operons upon exposure to high temperature (4, 5). Furthermore, heat shock induction controlled by the htpR gene appears to play a critical role in bacterial growth at high temperature and in acquired thermotolerance under certain conditions (4). The importance of htpR in heat shock induction and growth at high temperature was further substantiated by isolation and characterization of additional htpR mutants (6). The htpR gene has been cloned into multicopy plasmids, and its product has been identified as a protein with an apparent molecular weight of 33,000-36,000 (6, 7). The recombinant plasmids carrying htpR (or part thereof) hav...

Aggregation of heat-shock-denatured, endogenous proteins and distribution of the IbpA/B and Fda marker-proteins in Escherichia coli WT and grpE280 cells

“…Escherichia coli B178 WT (W3101 galE sup + ), E. coli B178 grpE280 [bearing the point mutation Gly 122 to Asp (Wu et al, 1994)] and E. coli CG459 rpoH-165 [the amber mutant, carrying a temperature-sensitive suppressor, supCts (Yura et al, 1984)], E. coli C600 thr leu supE and E. coli C600 grpE280 (Ang et al, 1986) were grown in LB. LB was supplemented with ampicillin (50 mg ml 21 ) for B178(pKEN8) and B178 grpE280(pKEN8) (Kȩdzierska et al, 2001).…”

The rpoE gene of Escherichia coli, which encodes sigma E, is essential for bacterial growth at high temperature

“…The primary factor, 70 encoded by rpoD, is responsible for transcription of the majority of the genes expressed during exponential growth. In addition, alternative factors direct transcription of sets of genes whose products are needed for specific functions, such as nitrogen fixation, flagellum synthesis, heat shock response, and stationary-phase growth (4).The activities of two alternative factors, 32 and E , increase after the cell is exposed to a high temperature or ethanol (2,3,5,21,25,28). RNA polymerase containing 32 (E 32 ) transcribes the heat shock genes whose products are related to chaperones and proteases (29).…”

“…The activities of two alternative factors, 32 and E , increase after the cell is exposed to a high temperature or ethanol (2,3,5,21,25,28). RNA polymerase containing 32 (E 32 ) transcribes the heat shock genes whose products are related to chaperones and proteases (29).…”

Inositol monophosphatase activity from the Escherichia coli suhB gene product

“…The suhB2(Cs) mutation is another allele of suhB and was isolated as an extragenic suppressor of the rpoH15(Ts) mutation. The rpoH15 mutant gene produces an altered 32 protein and causes a defect in the induction of heat shock proteins at higher temperatures (42). The suhB2(Cs) mutation rescued the temperature-sensitive cell growth of the rpoH15 mutant and partially restored heat shock induction in the mutant cell (40).…”