Saturated fatty acid mutant of Saccharomyces cerevisiae with an intact fatty acid synthetase.

A Saccharomyces cerevisiae conditional mutant, LK 181, is described which grows at 37 C only when supplemented with a saturated fatty acid of 12 to 14 carbon atoms chain length. At 22 C, however, no fatty acid supplementation is required for growth. The fatty acid concentration required for optimal growth at 37 C is about four times lower for LK 181 than for fatty acid synthetase-deficient mutants. In contrast to all fatty acid synthetase mutants so far examined, mutant LK 181 cannot grow with palmitic acid. The addition of palmitic, palmitoleic, or oleic acid to the culture medium prevents LK 181 growth at temperatures between 22 and 37 C. In vivo as well as in vitro, cellular de novo fatty acid biosynthesis from acetate is unimpaired in this mutant. It is suggested that endogenously synthesized fatty acids, due to their chain lengths of 16 and more carbon atoms, cannot supplement the mutant LK 181. It is concluded that the exogeneously supplied fatty acids act as allosteric effectors for a mutationally altered cellular protein to restore its biological function at elevated temperatures, rather than as a substitute for endogenously synthesized long-chain fatty acids.