DNA coding for extracellular glucoamylase genes STAI and STA3 was isolated from DNA libraries of two Saccharomyces diastaticus strains, each carrying STAI or STA3. Cells transformed with a plasmid carrying either the STAI or STA3 gene secreted glucoamylases having the same enzymatic and immunological properties and the same electrophoretic mobilities in acrylamide gel electrophoresis as those of authentic glucoamylases. Southern blot analysis of genomic DNA from S. diastaticus and a glucoamylase-non-secreting yeast, Saccharomyces cerevisiae, revealed that the STAI and STA3 loci of S. diastaticus showed a high degree of homology, and that both yeast species (S. diastaticus and S. cerevisiae) contained DNA segments highly homologous to those of the extracellular glucoamylase genes. Restriction maps of the homologous DNA segments suggested that the extracellular glucoamylase genes of S. diastaticus may have arisen from recombination among the resident DNA segments in S. cerevisiae.

We introduced the nuclei isolated from the respiration-sufficient killer strain of the yeast Saccharomyces cerevisiae into the yeast protoplasts prepared from the respiration-deficient non-killer strain with the aid of polyethylene glycol. The resulting karyoductants were respiration-deficient non-killers. Nuclear staining with ethidi~ bromide or DAPI and tetrad analysis of the k~oductan~ presented evidence that the nuclei introduced into protoplasts were fused to the resident nuclei, leading to stable diploids. This technique termed karyoduction will be useful in the study of nucleo-cytoplasmic relationship in yeast and other organisms. YeastFusion