A transposon-5 insertion library of Corynebacterium matruchotii ATCC14266 was generated and screened for mutants with altered corynomycolic acid content. One of these designated 319 mutants showed an interruption of a gene encoding an integral membrane protein. MALDI mass spectra of trehalose monocorynomycolate (TMCM), trehalose dicorynomycolate, and methyl corynomycolates derived from cell wall arabinogalactan-corynomycolate showed that these lipids from the mutant contained a lower amount of shortchain (C-24 to C-34) and much greater amount of long-chain (primarily C-36:2) corynomycolic acids than the wild type. An analysis of mRNA demonstrated that the integral membrane protein and ATP-binding cassette transporter are transcriptionally coupled. These results suggested that the proteins/enzymes encoded by the membrane transporter gene locus preferably move short-chain corynomycolic acids from the cytoplasm across the membrane bilayer to the periplasmic space where the synthesis of TMCM is thought to occur. This is the first evidence linking corynomycolic acid to a transporter gene locus. published by Elsevier Inc.