Polyketide synthase involved in the biosynthesis of 2,4-dimethyl-2-eicosenoic acid, a lipid component of the lipooligosaccharides (LOS) which are not located at the bacterial surface but rather in deeper compartments of the cell envelope of M.smegmatis. Lipid metabolism; fatty acid biosynthesis. Homodimer. Is organized in a condensing KS-AT and a modifying DH-PsiKR-ER-KR region, followed by a flexibly tethered ACP domain. Disruption of this gene abolishes the production of both 2,4-dimethyl-2-eicosenoic acid, a polymethyl-branched fatty acid (PMB-FA), and lipooligosaccharides (LOS). Complementation of the mutant with the wild-type gene fully restores the phenotype.