Disseminated Mycobacterium avium (Ma)-M. intracellulare disease is a p
revalent opportunistic infection in patients with Acquired Immune Defi
ciency Syndrome. Mycobacteria produce a variety of fatty acids which p
rovide the first line of defence against potentially lethal environmen
tal conditions. The metabolism of the branched-chain amino acids (BCAA
) could be correlated to the production of branched-chain fatty acids
in mycobacteria. In order to develop a better understanding of Mycobac
terium BCAA biosynthesis, three genes, ilvBN and ilvC, encoding acetoh
ydroxy acid synthase (AHS) and acetohydroxy acid isomeroreductase (IR)
, respectively, were cloned from Ma. The genes were isolated by screen
ing a Ma genomic library with a heterologous probe. The deduced amino
acid sequences revealed significant homology to the AHS and IR protein
s from other bacterial species.