Dissection of the heat-shock response in Mycobacterium tuberculosis using mutants and microarrays

Department of Infectious Diseases and Microbiology, Centre for Molecular Microbiology and Infection, Imperial College of Science Technology and Medicine, London SW7 2AZ, UK 1 School of Crystallography, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK 2 Department of Medical Microbiology, St George’s Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK 3 Author for correspondence: Graham Stewart. Tel: +44 207 594 3090. Fax: +44 207 594 3095. e-mail: g.stewart{at}ic.ac.uk Regulation of the expression of heat-shock proteins plays an important role in the pathogenesis of Mycobacterium tuberculosis . The heat-shock response of bacteria involves genome-wide changes in gene expression. A combination of targeted mutagenesis and whole-genome expression profiling was used to characterize transcription factors responsible for control of genes encoding the major heat-shock proteins of M. tuberculosis . Two heat-shock regulons were identified. HspR acts as a transcriptional repressor for the members of the Hsp70 (DnaK) regulon, and HrcA similarly regulates the Hsp60 (GroE) response. These two specific repressor circuits overlap with broader transcriptional changes mediated by alternative sigma factors during exposure to high temperatures. Several previously undescribed heat-shock genes were identified as members of the HspR and HrcA regulons. A novel HspR-controlled operon encodes a member of the low-molecular-mass -crystallin family. This protein is one of the most prominent features of the M. tuberculosis heat-shock response and is related to a major antigen induced in response to anaerobic stress. Keywords: HspR, HrcA, Hsp70, Hsp60, transcriptional regulator Abbreviations: ADC, albumin/dextrose (glucose)/catalase; CIRCE, controlling inverted repeat of chaperone expression; HAIR, HspR-associated inverted repeat; OADC, oleic acid/dextrose (glucose)/albumin/catalase a A list of the 100 ORFs most highly induced by heat shock is provided as supplementary data with the online version of this paper (http://mic.sgmjournals.org).