BIOCHEMICAL AND PHYLOGENETIC ANALYSES OF METHIONYL-TRANSFER-RNA SYNTHETASE ISOLATED FROM A PATHOGENIC MICROORGANISM, MYCOBACTERIUM-TUBERCULOSIS

Mycobacterium tuberculosis methionyl-tRNA synthetase (MetRS) has been cloned and characterized. The protein contains class I signature seque nces but lacks the Zn2+ binding motif and the C-terminal dimerization appendix that are found in MetRSs from several organisms including E. coli MetRS. Consistent with these features, the enzyme behaved as a mo nomer in a gel filtration chromatography and did not contain the bound Zn2+. Nonetheless, it was active to the tRNA(Met) of E. coli as deter mined by in vivo genetic complementation and in vitro reaction. Phylog enetic analysis separated the M. tuberculosis and E. coli MetRSs into prokaryote and eukaryote-archaea group, respectively. This result is c onsistent with the taxonomic locations of the organism but is an inter esting contrast to the case of its paralogous protein, isoleucyl-tRNA synthetase, and suggests that the two enzymes evolved in separate idio syncratic pathways. (C) 1998 Federation of European Biochemical Societ ies.