| Abstrakt: |
Among 52 Saccharomyces cerevisiae fatty acid synthetase (fas)mutants screened for their ability to incorporate 14C-labeled pantothenic acid into the fatty acid synthetase multienzyme complex, especially those of fas-complementation group VII had lost this ability. The purified fatty acid synthetase complexes of all the 19 fas-mutants available from this group were shown to be free of 14C-labeled pantothenic acid. The amount of pantothenate incorporated into the enzymes of several other fas-mutants of the non-pleiotropic complementation groups II, V, VI and VIII, however, was similar to that observed with wild-type fatty acid synthetase. The purified pantothenate-free fatty acid synthetases of five different group VII fas-mutants have been tested for the seven known component enzymes of the complex. In all mutants, only the β-ketoacyl synthetase was inactive whereas in vitro all the other partial activities were unimpaired. By sodium dodecylsulfate-polyacrylamide-gel electeophoresis, no differences could be observed between the protein structure of the pantothenate-free mutant fatty acid synthetase and that of the wild-type comp ex. Both were separated into three different components A, B and C with molecular weights of 185000, 180000 and 177000, respectively. However, some fas-mutants consist only of the components A and B, others only of B and C. The study of various [14C]pantothenate-labeled mutant fatty acid synthetases suggests that component C originates from A presumably by limited proteolysis. In the undegraded complex AB, [14C]pantothenate is only associated with the component A. Since in one of the mutants studied A is completely converted to C, it is concluded that A is one distinct component rather than a group of components with identical molecular weights. It is tentatively suggested that the gene product of fas 2, one of the two known fatty-acid-synthetase gene clusters in yeast, is only one, single and multifunctional polypeptide chain. Therefore, it appears that in yeast, the acyl carrier protein is not an individual protein component of the fatty acid synthetase complex, but only a distinct region of the multifunctional polypeptide chain encoded by fas 2. [ABSTRACT FROM AUTHOR] |
