The clpB ATPase of Streptomyces albus G belongs to the HspR heat shock regulon

The clpB gene of Streptomyces albus was cloned by polymerase chain reaction (PCR) using degenerate oligonucleotides, Transcriptional analysis showed that the clpB gene was heat induced. Primer extension identified a transcription start site preceded by typical vegetative -10 and -35 hexamer sequences. The Streptomyces HspR repressor is known to bind to three inverted repeat motifs (IR1, IR2, IR3) upstream from the S. coelicolor dnaK operon. We identified an inverted repeat motif identical to IR3 upstream from the S. albus clpB gene. DNA-binding experiments showed that HspR regulates clpB transcription by interacting directly with this motif. Streptomyces albus is the first Gram-positive organism for which the co-regulation of DnaK and ClpB has been described. Such co-regulation suggests that there is a physiological relationship between these two proteins in this bacterium. Genes similar to hspR were also identified in Mycobacterium leprae, M. tuberculosis and in bacteria unrelated to the actinomycetales order, such as Helicobacter pylori and Aquifex aeolicus. HspR binding sites were found in these bacteria upstream from various heat shock genes, suggesting that these genes are regulated by HspR. The HspR binding site, here called HAIR (HspR associated inverted repeat), has the consensus sequence CTTGAGT N7 ACTCAAG.