RESUMO
SETTING: Molecular Research Laboratory, Department of Medical Microbiology, University of Cape Town and Groote Schuur Hospital. OBJECTIVE: Characterize Mycobacterium tuberculosis homologue of the Streptomyces coelicolor, sporulation specific, whiB regulatory gene. DESIGN: The M. tuberculosis whiB3 gene was isolated by enriched cloning of a 2.8 kb BamHl fragment to which the S. coelicolor whiB gene hybridized. Expression of the gene was analysed by S1 nuclease analysis and promoter studies. RESULTS: An open reading frame within the 2.8 kb BamHl fragment was identified as the M. tuberculosis whiB3 gene, one of four whiB homologues in the M. tuberculosis genome. The deduced amino acid sequence has a 92% identity with a M. leprae protein, and 32% identity with the S. coelicolor WhiB protein. S1 nuclease analysis showed that the M. tuberculosis whiB3 gene is constitutively expressed by the cells in liquid culture. Primer extension analysis revealed three transcriptional start sites. Expression from the three potential promoters is growth phase-dependent. CONCLUSION: The M. tuberculosis whiB3 gene is expressed throughout growth, but expression from the individual promoters is growth phase dependent.