IDENTIFICATION OF A CAULOBACTER-CRESCENTUS OPERON ENCODING HRCA, INVOLVED IN NEGATIVELY REGULATING HEAT-INDUCIBLE TRANSCRIPTION, AND THE CHAPERONE GENE GRPE

In response to elevated temperature, both prokaryotic and eukaryotic c ells increase expression of a small family of chaperones, The regulato ry network that functions to control the transcription of the heat sho ck genes in bacteria includes unique structural motifs in the promoter region of these genes and the expression of alternate sigma factors, One of the conserved structural motifs, the inverted repeat CIRCE elem ent, is found in the 5' region of many heat shock operons, including t he Caulobacter crescentus groESL operon, We report the identification of another C. crescentus heat shock operon containing two genes, hrcA (hrc for heat shock regulation at CIRCE elements) and a grpE homolog, Disruption of the hrcA gene, homologs of which are also found upstream of grpE in other bacteria, increased transcription of the groESL oper on, and this effect was dependent on the presence of an intact CIRCE e lement, This suggests a role for HrcA in negative regulation of heat s hock gene expression, We identified a major promoter transcribing both hrcA and grpE and a minor promoter located within the hrcA coding seq uence just upstream of grpE, Both promoters were heat shock inducible, with maximal expression 10 to 20 min after heat shock, Both promoters were also expressed constitutively throughout the cell cycle under ph ysiological conditions, C. crescentus GrpE, shown to be essential for viability at low and high temperatures, complemented an Escherichia co li Delta grpE strain in spite of significant differences in the N- and C-terminal regions of these two proteins, demonstrating functional co nservation of this important stress protein.