hrcA, the first gene of the Bacillus subtilis dnaK operon encodes a negative regulator of class I heat shock genes

Abstract

Whereas in Escherichia coli only one heat shock regulon is transiently induced by mild heat stress, for Bacillus subtilis three classes of heat shock genes regulated by different mechanisms have been described. Regulation of class I heat shock genes (dnaK and groE operons) involves an inverted repeat (CIRCE element) which most probably serves as an operator for a repressor. Here, we report on the analyses of an hrcA null mutant (⌬hrcA), in which hrcA, the first gene of the dnaK operon, was deleted from the B. subtilis chromosome. This strain was perfectly viable at low and high temperatures. Transcriptional analysis of the deletion mutant revealed a high level of constitutive expression of both the dnaK and groE operons even at a low temperature. A further increase in the amount of groE transcript was observed after temperature upshift, suggesting a second induction mechanism for this operon. Overproduction of HrcA protein from a second copy of hrcA derived from a plasmid (phrcA ؉ ) in B. subtilis wild-type and ⌬hrcA strains prevented heat shock induction of the dnaK and groE operons at the level of transcription almost completely and strongly reduced the amounts of mRNA at a low temperature as well. Whereas the wild-type strain needed 4 h to resume growth after temperature upshift, the ⌬hrcA strain stopped growth only for about 1 h. Overproduction of HrcA protein prior to a heat shock almost completely prevented growth at a high temperature. These data clearly demonstrate that the hrcA product serves as a negative regulator of class I heat shock genes.The heat shock response is an important homeostatic mechanism that enables cells from animals, plants, and bacteria to survive a variety of environmental stresses (21,22). It is characterized by the transiently increased synthesis of a number of proteins, which are called heat shock proteins (HSPs). The strong evolutionary conservation of the heat shock response argues that this response is beneficial for many kinds of cells. HSPs have essential roles in the synthesis, transport, and folding of proteins and are often referred to as molecular chaperones (9). In prokaryotes, the major HSPs are encoded by single genes expressed constitutively at all temperatures. Following a temperature upshift, the rates of expression of these genes abruptly accelerate. After about 8 min, the rates of synthesis of the HSPs are turned down. In Escherichia coli, the heat shock response is positively regulated by the alternate sigma factor 32 and is negatively regulated by the products of the heat shock genes dnaK, dnaJ, and grpE (for recent reviews, see references 5 and 39).In contrast to E. coli, Bacillus subtilis contains three classes of heat shock genes which are turned on by mild heat stress (12). Class I heat shock genes, as exemplified by the dnaK and the groE operons, are expressed from the vegetative promoter P A (6), and their expression involves a cis-active inverted repeat called CIRCE (41). We suggested that class I heat shock genes are negatively regulated by a repressor...

Role for dnaK locus in tolerance of multiple stresses in Staphylococcus aureus

“…Class I Hsps comprise the classical Hsps that are encoded by genes of the groES/EL and dnaK operons, and cellular levels of these proteins are controlled by the HrcA repressor (Schulz & Schumann, 1996). Class II Hsps are s B dependent, and are induced by heat and other stresses (Schulz & Schumann, 1996). Class III Hsps are Clp proteases/ ATPases, and are typically under the control of the transcriptional repressor CtsR (Derre et al, 1999).…”

“…subtilis, at least four classes of Hsps have been identified based on their regulatory mechanisms. Class I Hsps comprise the classical Hsps that are encoded by genes of the groES/EL and dnaK operons, and cellular levels of these proteins are controlled by the HrcA repressor (Schulz & Schumann, 1996). Class II Hsps are s B dependent, and are induced by heat and other stresses (Schulz & Schumann, 1996).…”

The heat-shock response of Listeria monocytogenes comprises genes involved in heat shock, cell division, cell wall synthesis, and the SOS response

“…Maintenance of protein quality is important for normal growth of cells and is essential under stress conditions. In L. monocytogenes, two specific heat-shock-response mechanisms and a general stress-response mechanism can be distinguished, namely, the class I and class III heat-shock response, and the class II stress response (Benson & Haldenwang, 1993;Kruger & Hecker, 1998;Schulz & Schumann, 1996). Class I heat-shock genes are controlled by the HrcA repressor, which binds to the CIRCE operator sequence (TTAGCACTC-N 9 -GAGTGCTAA) preceding this class of genes.…”

Disruption of hspR, the repressor gene of the dnaK operon in Streptomyces albus G

“…In B. subtilis, the upstream gene of the dnaK operon is hrcA, which codes for a protein of 39 kDa (Schulz and Schumann, 1996;Wetzstein et al, 1992). The hrcA (heat regulation at CIRCE) product interacts directly with a CIRCE-bearing DNA fragment (Yuan and Wong, 1995a).…”