The Mycobacterium tuberculosis mysB gene product is a functional equivalent of the Escherichia coli sigma factor, KatF

Mycobacterium tuberculosis, the causative agent of tuberculosis, may remain dormant within its host for many years. The nature of this dormant or late nt state is not known, but it may be a specializeti form of the stationary growth phase. In Escherichia coli, KatF (or RpoS) is the major stationary p hase sigma factor regulating an array of genes expressed in this phase of g rowth. A potential M. tuberculosis katF homologue was cloned using a fragme nt of the E. coli katF gene as a probe. DNA sequence analysis of a resultan t clone showed 100% identity to a fragment of DNA encoding the hi. tubercul osis mysA and mysB genes. Overexpression of mysB in M. bovis BCG resulted i n an increase in katG mRNA and catalase and peroxidase activity, and an inc rease in sensitivity of the cells to isoniazid. An increase in katG promote r activity from a reporter vector was demonstrated when mysB was overexpres sed from the same plasmid, indicating a direct relationship between MysB an d katG expression. (C) 1999 Published by Elsevier Science B.V. All rights r eserved.