Stability of recombinant plasmids containing the ars sequence of yeast extrachromosomal rDNA in several strains of Saccharomyces cerevisiae

Abstract

The mitotic stabilities of hybrid plasmid Rcp21/11, which contains the replicator of yeast rDNA, have been compared for four yeast host strains of different origins. In two related strains, Saccharomyces cerevisiae A62-1G-P188 and 1A-P3812 from the Peterhof genetic stocks, the plasmid was much more stable than in strains DC5 and GRF18 from the USA stocks. The enhanced mitotic stability of Rcp21/11 in these two yeast strains is obviously attributable to a higher rate of integration of the plasmid into the chromosomal rDNA repeats of the hosts. The centromeric locus CEN3 was inserted into Rcp21/11 because it provides high mitotic and meiotic stability of plasmids with yeast replicators, due to an ordered distribution of plasmids throughout cell division. Using the new centromeric plasmid Rcp CEN3, transformation of the four above-described yeast strains was carried out. It was found that, similarly to centromeric plasmids with other chromosomal replicators, Rcp CEN3 remains in the cell as a single copy. In strains DC5, GRF18 and A62-1G-P188 the mitotic stability of Rcp CEN3 was 20–50%, i.e., less than half that of plasmids containing locus CEN3 and other yeast repliiators, ars1, ars2 and the 2μ DNA replicator. The mitotic stability of Rcp CEN3 in strains 1A-P3812 (from the Peterhof genetic stocks) for individual clones reached 85%, i.e. close to that of the other plasmids. Genetic analysis showed that the capacity of strain 1A-P3812 to stably retain Rcp CEN3 has a recessive polygenic character. We suggest that the observed differences in mitotic stability of centromeric plasmid Rcp CEN3 between various yeast strains reflects the differences in activity of rDNA replicator in these strains. The nature of extrachromosomal rDNA circles, found in some strains of S. cerevisiae, is discussed from the point of view of the data.