[Genetic analysis of the mutant RD-50 in Saccharomyces cerevisiae. The role of nuclear and mitochondrial mutation].

Inheritance of the mutant phenotype of respiratory deficience in RD-50 strain was studied. The deficience can be restored, giving respiratory sufficience, in crosses with rho0 testers. The "restorable" phenotype of the mutant, named RDc+, was shown to be determined by a nuclear pet-like mutation (pet50). The restorable RDc+ phenotype is stabilized in the presence of the pet50 allele, but can remain as such in the presence of the wild-type allele PET50. Restoration also takes place in cytoductants with the nucleus of kar partner. In order to explain the behaviour of the mitochondrial mutation mit50, we suppose it to be a microdeletion, capable of reversion, due to integration of a putative mt episome. Some features of the nuclear mutation pet50, particularly, its segregation in mitotic progeny of some revertants to respiratory competence point to its peculiarity. We suppose the mutation pet50 to be an insertion into the chromosomal PET50 gene. This insertion may be excised, remaining within the cell in the free state for some time, and then either eliminate or reintegrate into the chromosome.