Cloning and characterization of arylamine N-acetyltransferase genes from Mycobacterium smegmatis and Mycobacterium tuberculosis: Increased expressionresults in isoniazid resistance

Arylamine N-acetyltransferases (NATs) are found in many eukaryotic organism s, including humans, and have previously been identified in the prokaryote Salmonella typhimurium. NATs from many sources acetylate the antitubercular drug isoniazid and sol inactivate it. nut genes were cloned from Mycobacte rium smegmatis and Mycobacterium tuberculosis, and expressed in Escherichia coli and M. smegmatis. The induced M. smegmatis NAT catalyzes the acetylat ion of isoniazid. A monospecific antiserum raised against pure NAT from S. typhimurium recognizes NAT from M. smegmatis and cross-reacts with recombin ant NAT from M. tuberculosis. Overexpression of mycobacterial nat genes in E. coli results In predominantly insoluble recombinant protein; however, wi th M. smegmatis as the host using the vector pACE-1, NAT proteins from M. t uberculosis and M. smegmatis are soluble. M. smegmatis transformants induce d to express the M. tuberculosis nat gene in culture demonstrated a threefo ld higher resistance to isoniazid. We propose that NAT in mycobacteria coul d have a role in acetylating, and hence inactivating, isoniazid.