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Molecular Basis of the Defective Heat Stress Response in Mycobacterium leprae ^,

Molecular Biology Research Dept., Laboratory Research Branch, National Hansen's Disease Programs at LSU-SVM, Baton Rouge, Louisiana,¹ Laboratory of Bacterial Pathogenesis and Immunology, The Rockefeller University, New York, New York,² Dept. Veterinary Clinical Sciences, LSU School of Veterinary Medicine, Baton Rouge, Louisiana,³ TB Center, Public Health Research Institute, Newark, New Jersey,⁴ Division of Infectious Diseases, Children's Hospital, and Harvard Medical School, Boston, Massachusetts⁵

Received 18 April 2007/ Accepted 28 September 2007

Mycobacterium leprae, a major human pathogen, grows poorly at 37°C. The basis for its inability to survive at elevated temperatures was investigated. We determined that M. leprae lacks a protective heat shock response as a result of the lack of transcriptional induction of the alternative sigma factor genes sigE and sigB and the major heat shock operons, HSP70 and HSP60, even though heat shock promoters and regulatory circuits for these genes appear to be intact. M. leprae sigE was found to be capable of complementing the defective heat shock response of mycobacterial sigE knockout mutants only in the presence of a functional mycobacterial sigH, which orchestrates the mycobacterial heat shock response. Since the sigH of M. leprae is a pseudogene, these data support the conclusion that a key aspect of the defective heat shock response in M. leprae is the absence of a functional sigH. In addition, 68% of the genes induced during heat shock in M. tuberculosis were shown to be either absent from the M. leprae genome or were present as pseudogenes. Among these is the hsp/acr2 gene, whose product is essential for M. tuberculosis survival during heat shock. Taken together, these results suggest that the reduced ability of M. leprae to survive at elevated temperatures results from the lack of a functional transcriptional response to heat shock and the absence of a full repertoire of heat stress response genes, including sigH.

Published ahead of print on 12 October 2007.

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