Salicylate uniquely induces a 27-kDa protein in tubercle bacillus

Salicylate was found to uniquely induce a 27-kDa protein in Mycobacterium tuberculosis complex organisms but not in Mycobacterium smegmatis or Escherichia coli. The structural analogue antitubercular para-amino-salicylate also induced the 27-kDa protein but to a somewhat lower level than salicylate. Other structural analogues such as benzoic acid and acetyl salicylic acid (aspirin) did not induce the 27-kDa protein. Western blot analysis indicated that the 27-kDa protein was localized mainly in the cytoplasm. The 27-kDa protein was not expressed at different growth phases in the absence of salicylate. The 27-kDa protein was identified as a putative benzoquinone methyltransferase (Rv0560c), which has several homologues in the M. tuberculosis genome. The cloned 27-kDa gene was found to express constitutively in E. coli, M. smegmatis and BCG with or without salicylate.