Cloning, sequencing and characterization of a fatty acid synthase-encoding gene from Mycobacterium tuberculosis var....

Mycobacterial cell walls contain unique lipids such as mycolic acids, very long chain fatty acids and multimethyl-branched fatty acids. A multifunctional fatty acid synthase (Fas) with the unique capability of catalyzing both de novo synthesis and chain elongation of fatty acids has been purified and characterized from Mycobacterium tuberculosis var. bovis BCG (Bacillus Calmette-Geurin) [Kikuchi et al., Arch. Biochem. Biophys. 295 (1992) 318-326]. To understand how the various domains that catalyze the reactions involved in both de novo synthesis and elongation are organized in the mycobacteria, a fas gene was cloned from a cosmid library of genomic DNA from M. bovis BCG. Sequencing of the cosmid clone revealed a contiguous sequence of 11 577 bp of mycobacterial genome containing a 8389-bp open reading frame that could code for a protein of 2797 amino acids (301 kDa). By comparing the Fas aa sequence with the sequences in the active site regions of known fas and polyketide synthase-encoding genes, the functional catalytic domains in Fas were identified. This analysis revealed that the domains are organized in the following order: acyltransferase, enoyl reductase, dehydratase, malonyl/palmitoyl transferase, acyl carrier protein, beta-keto reductase, beta-ketoacyl synthase. This domain organization is like a head to tail fusion of the two yeast fas gene subunits. The results obtained constitute the first report of the cloning, sequencing and structural elucidation of a fas from the Mycobacteria.