ISOLATION OF A SACCHAROMYCES-CEREVISIAE LONG-CHAIN FATTY ACYL-COA SYNTHETASE GENE (FAA1) AND ASSESSMENT OF ITS ROLE IN PROTEIN N-MYRISTOYLATION

Regulation of myristoylCoA pools in Saccharomyces cerevisiae plays an important role in modulating the activity of myristoylCoA:protein N-myristoyltransferase (NMT), an essential enzyme with an ordered Bi Bi reaction that catalyzes the transfer of myristate from myristoylCoA to greater-than-or-equal-to 12 cellular proteins. At least two pathways are available for generating myristoylCoA: de novo synthesis by the multifunctional, multisubunit fatty acid synthetase complex (FAS) and activation of exogenous myristate by acylCoA synthetase. The FAA1 (fatty acid activation) gene has been isolated by genetic complementation of a faa1 mutant. This single copy gene, which maps to the right arm of chromosome XV, specifies a long chain acylCoA synthetase of 700 amino acids. Analyses of strains containing NMT1 and a faa1 null mutation indicated that FAA1 is not essential for vegetative growth when an active de novo pathway for fatty acid synthesis is present. The role of FAA1 in cellular lipid metabolism and protein N-myristoylation was therefore assessed in strains subjected to biochemical or genetic blockade of FAS. At 36-degrees-C, FAA1 is required for the utilization of exogenous myristate by NMT and for the synthesis of several phospholipid species. This requirement is not apparent at 24 or 30-degrees-C, suggesting that S. cerevisiae contains another acylCoA synthetase activity whose chain length and/or temperature optima may differ from Faalp.