Killer DNA plasmids of the yeast Kluyveromyces lactis : III. Plasmid recombination.

The killer character of Kluyveromyces lactis is cytoplasmically inherited. Two DNA plasmids k1 and k2 (8.8 and 13.4 kilobase pairs, respectively) are associated with the killer system. Either cytoplasmic or nuclear mutations can lead to a loss of the killer activity. Two cytoplasmic non-killer mutants have been specifically studied. When they were crossed to each other, the killer phenotype was restored. Genetic analysis led us to conclude that each of the two mutants carried a mutation in the k1 plasmid and that the recovery of killer phenotype was due to genetic recombination of the plasmids, and not to complementation.