Genetic changes in yeast cells cotransformed with mitochondrial DNA and plasmid YEp13 are not elicited by recombinant molecules made by covalent insertion of mitochondrial DNA into YEp13

Abstract

Saccharomyces cerevisiae strain DC5-E2 that lacks mtDNA ( leu2 rho o ) can be cotransformed with a mixture of mtDNA and the plasmid YEp13 (LEU2/2μ/pBR322) to produce Leu + transormants which, on being mated to mit − tester strains, generate respiratory competent diploids (such events are denoted marker rescue). In this work strain DC5-E2 was transformed with recombinant molecules consisting of a mtDNA segment including the oli2 gene inserted into YEp13. The Leu + transformants made with the recombinant plasmids were unable to rescue mit − testers carrying mutations in the oli2 region, in contrast to Leu + cotransformants made with mixtures of YEp13 and oli2 mtDNA. We conclude that marker rescue events occur as a result of interactions between the mtDNA of the mit − tester and the mtDNA sequences introduced by transformation. Such interactions cannot occur when the latter mtDNA is forced to replicate in covalent association with YEp13, probably in the nucleus.