The acyl-CoA synthetases encoded within FAA1 and FAA4 in Saccharomyces cerevisiae function as components of the fatty acid transport system linking import, activation, and intracellular utilization

Exogenous long-chain fatty acids are activated to coenzyme A derivatives pr ior to metabolic utilization. In the yeast Saccharomyces cerevisiae, the ac tivation of these compounds prior to metabolic utilization proceeds through the fatty acyl-CoA synthetases Faa1p and Faa4p. Faa1p or Faa4p are essenti al for long-chain fatty acid import, suggesting that one or both of these e nzymes are components of the fatty acid transport system, which also includ es Fat1p. By monitoring the intracellular accumulation of the fluorescent l ong-chain fatty acid analogue 4,4-difluoro-5-methyl-4-bora-3a,4a-diazas-ind acene-3-dodecanoic acid, long-chain fatty acid transport was shown to be se verely restricted in a faa1 Delta faa4 Delta strain. These data established for the first time a mechanistic linkage between the import and activation of exogenous fatty acids in yeast. To investigate this linkage further, ol eoyl CoA levels were defined following incubation of wild type and mutant c ells with limiting concentrations of exogenous oleate. These studies demons trated oleoyl CoA levels were reduced to less than 10% wild-type levels in faa1 Delta and faa1 Delta faa4 Delta strains. Defects in metabolic utilizat ion and intracellular trafficking were also found in the fatty acyl-CoA syn thetase-deficient strains. The faa1 Delta faa4 Delta strain had a marked re duction in endogenous acyl-CoA pools, suggesting these enzymes play a role in maintenance of endogenous acyl-CoA pools, metabolism and trafficking. In addition, this strain had levels of in vivo beta -oxidation of exogenous o leate reduced 3-fold when compared with the isogenic parent. Northern analy ses demonstrated an additional defect in fatty acid trafficking as FAA1 or FAA4 were required for the transcriptional regulation of the genes encoding the peroxisomal enzymes acyl-CoA oxidase (POX1) and medium-chain acyl-CoA synthetase (FAA2). These data support the hypothesis that fatty acyl-CoA sy nthetase (Faa1p or Faa4p) functions as a component of the fatty acid import system by linking import and activation of exogenous fatty acids to intrac ellular utilization and signaling.