Isolated and/or recombinant nucleic acids encoding mycobacterial methionyl-tRNA synthetase have been characterized. Recombinant DNA constructs and vectors having a sequence which encodes mycobacterial methionyl-tRNA synthetase have been made, and can be used for the construction of tester strains as well as for the production of isolated and/or recombinant methionyl-tRNA synthetases. These enzymes or portions thereof are useful in the biochemical separation of methionine and quantification of methionine or ATP, and for producing antibodies useful in the purification and study of the enzyme, for example. Host cells and methods useful for producing recombinant mycobacterial methionyl-tRNA synthetases are described, as are tester strains, which are cells engineered to rely on the function of the tRNA synthetase encoded by an introduced cloned gene. Tester strains can be used to identify inhibitors of the essential tRNA synthetase enzyme encoded by the introduced cloned gene, and thus provide a means to assess the antimicrobial effect and specificity of the inhibitor without employing slow-growing, pathogenic strains of mycobacteria, such as Mycobacterium tuberculosis.