Alignment of selected methionine adenosyltransferase sequences. The following sequences were aligned with the Clustal algorithm: Mt, M. tuberculosis; Ms, M. smegmatis; Mb, M. bovis; Mm, M. marinum; Ml, M. leprae; Ma, M. avium; Bs, Bacillus subtilis ; Ec, Escherichia coli MetK , Sc, Saccharomyces cerevisiae SAM1 ; Hs, Homo sapiens MAT1 . Residues conserved by 75% of these sequences are boxed. The annotation below refers to 100% (#) or 98% (+) conservation of residues by the 117 sequences in Figure 2. Residues marked with M are the putative Mg2+ binding sites, K the putative K+ binding sites, A the ATP-binding residues of the P-loop, and X the residues that interact with the methionine substrate.