Mutants of that are unable to initiate sporulation, but can continue vegetative growth under conditions in which the wild-type strain sporulates, have been isolated and characterized. The mutations arose spontaneously as suppressors of the mutations, restoring the ability of mutants to grow on glycerol, and also spontaneously in cultures of a wild-type diploid strain undergoing sporulation in continuous culture. The mutations all conferred asporogeny, and were recessive in this respect to the wild-type, but dominant in acting as suppressors of the mutation. They fell into three complementation groups which corresponded to three unlinked loci, designated and None of these mutations was closely linked to the other initiation mutations defined by the loci, nor to the cell size control mutations and Loose linkage was detected between and , and and were linked to their respective centromeres. The and mutations are not nonsense suppressors. Mutations in all three genes conferred similar highly pleiotropic phenotypes including: asporogeny; dominant suppression of both and mutations; aberrant cell morphology and viability loss on starvation; constitutive ability to reduce tetrazolium (which is subject to carbon source repression in the wild-type); and complete repression of the synthesis of several polypeptides that are subject to carbon source repression in the wild-type strain and derepressed in mutants derepressed for sporulation. A diploid strain homozygous for the mutation did not undergo either premeiotic DNA replication or meiotic recombination when transferred to sporulation media.


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