Intergeneric transfer of deoxyribonucleic acid killer plasmids, pGKl1 and pGKl2, from Kluyveromyces lactis into Saccharomyces cerevisiae by cell fusion

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Abstract
Two novel linear DNA plasmids, pGKl1 and pGKl2, were isolated from the yeast K. lactic. K. lactis strains harboring the pGKl plasmids killed a certain group of yeasts, including S. cerevisiae, S. italicus, S. rouxii, K. lactis, K. thermotolerans, K. vanudenii, Torulopsis glabrata, Candida utilis and C. intermedia. In this experiment, the pGKl1 and pGKl2 plasmids were intergenerically transferred from a K. lactis killer strain into a nonkiller (killer-sensitive) strain of S. cerevisiae by the use of a protoplast fusion technique. Both of the pGKl plasmids replicated autonomously and stably in the new host cells of S. cerevisiae and could coexist with the resident 2-.mu.m DNA plasmid. The S. cerevisiae cells which accepted the pGKl plasmids expressed the same killer phenotype as that of the donor K. lactis killer and became resistant to the K. lactis killer. The pGKl plasmids existing in the S. cerevisiae cells were cured by treatment with ethidium bromide and the killer and resistance characters were simultaneously lost. The killer and the resistance genes are apparently located on the pGKl plasmids.