CODON USAGE IN THE MYCOBACTERIUM-TUBERCULOSIS COMPLEX

The usage of alternative synonymous codons in Mycobacterium tuberculos is (and M. bovis) genes has been investigated. This species is a membe r of the high-Ci + C Gram-positive bacteria, with a genomic G + C cont ent around 65 mol%, This G + C-richness is reflected in a strong bias towards C- and G-ending codons for every amino acid: overall, the G C content at the third positions of codons is 83 %. However, there is significant variation in codon usage patterns among genes, which appea rs to be associated with gene expression level. From the variation amo ng genes, putative optimal codons were identified for 15 amino acids. The degree of bias towards optimal codons in an M. tuberculosis gene i s correlated with that in homologues from Escherichia coli and Bacillu s subtilis, The set of selectively favoured codons seems to be quite h ighly conserved between M. tuberculosis and another high-G + C Gram-po sitive bacterium, Corynebacterium glutamicum, even though the genome a nd overall codon usage of the latter are much less G + C-rich.