MUTANT OF SACCHAROMYCES-CEREVISIAE DEFECTIVE FOR NUCLEAR FUSION

A mutant unable to fuse nuclei during mating was isolated from standard wild-type S. cerevisiae. Tetrad analysis of the mutation responsible for this defect (karl-1) shows that it segregates as a single Mendelian factor. The defect in karl-1 appears to be nuclear limited. Cytological and genetic evidence shows that in this mutant the events associated with zygote formation are normal until the point of nuclear fusion. The consequence of this defect is the formation of a multinucleate zygote which in subsequent divisions can segregate heterokaryons and haploid heteroplasmons.