Of 43 non-complementing alleles studied of the Saccharomyces cerevisiae fatty acid synthetase locus fas 1, 27 are reverted by external suppressors whereas 16 are susceptible only to intragenic suppression. Of the externally suppressible mutants 12 are reverted by both, amber and ochre suppressors, another 12 only by amber suppressors, and 3 are not suppressed by either of them. According to their response to the acridine mustard, ICR-191, one of the mutants not suppressible by external suppressors appears to be a frameshift mutation, whereas the others are suggested to be missense mutations. By X-ray induced mitotic recombination a genetic fine structure map of the complementing as well as of the non-complementing fas 1-alleles was constructed. It was found that the alleles of the non-pleiotropic complementation groups II, Va, Vb and Vc map at distinct and characteristic regions within fas 1, each of them covering 9.8, 13.5, 5.3 and 1.6 X-ray map units, respectively. On the other hand, the non-complementing fas 1-alleles are distributed randomly over the entire locus, no matter whether they were nonsense or missense mutations. These non-complementing alleles are spread over a DNA region of 72 X-ray map units length and all the complementing alleles studied map within this region. These results suggest that fas 1 encodes only one, functionally complex, polypeptide chain.

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Journal Article

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Tauro P, Holzner U, Castorph H, Hill F, Schweizer E

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