Control of fatty-acid synthetase biosynthesis in Saccharomyces cerevisiae.

143 out of 308 fas1 mutants (47%) and 139 out of 443 fas2-mutants (32%) genetically studied in this laboratory fail to complement with any other fas-mutant (deficient in fatty acid synthetase) of the same gene locus. From these noncomplementing fas-mutants no mutant fatty acid synthetase can be isolated using the wild-type enzyme purification procedure. Furthermore the noncomplementing fas-mutants generally contain no material immunologically crossreacting with a specific fatty acid synthetase antiserum. However, subunits obtained after dissociation of the complex with sodium dodecylsulfate still cross react with this antiserum. Therefore, it is concluded that noncomplementing fas-mutants contain no fatty acid synthetase component proteins, though one of the two fas-loci is mutationally unaffected. This conclusion was further confirmed by 14C-labeled amino acid incorporation studies which indicated that in noncomplementing fas-mutants, other than in wild type and complementing fas-mutant cells, no label was incorporated into fatty acid synthetase subunits or precursor proteins. At nonpermissive temperature, the same biochemical and immunological characteristics were observed with temperature-sensitive non-complementing fas-mutants. These results suggest that noncomplementing fas-mutants either represent regulatory mutants unable to induce the mutationally unaffected other fas-gene locus or that they are association-defective mutants. In both cases the resulting individual subunits of the complex may be rapidly degraded by intracellular proteases.