Gene Linkage and Gene-Enzyme Relations in the Fatty-Acid-Synthetase System of <em>Saccharomyces cerevisiae</em>.

In Saccharomyces cerevisiae, the genetic linkage as well as the biochemical characteristics of nine different fatty-acid-synthetase complementation groups have been studied. By spore tetrad analysis, the alleles of these nine groups were established to be located on three genetically unlinked DNA regions on the yeast genome. These regions consist of one separate gene and two clusters comprising two and three adjacent cistrons, respectively. In both clusters the alleles are closely linked within less than one map unit. The cistrons of the first cluster can be assigned to structural genes of the dehydratase and the second reductase, those of the second cluster to the first reductase and two proteins involved in the condensation reaction. Mutants of the separate fascistron produce a fully active fatty acid synthetase complex with all the component enzyme activities unimpaired under the assay conditions employed. The function of the gene product of this cistron is unknown, so far. From the pleiotropic fas-mutants, a fatty-acid-synthetase complex with residual component enzyme activities could not be isolated. It is concluded that, due to the polar transcription of the clustered cistrons in these mutants either none or only an incomplete aggregate is formed with the concomitant inactivation of residual component enzymes. [ABSTRACT FROM AUTHOR]