The CDC6 gene is required for centromeric, episomal, and 2-microns plasmid stability in the yeast Saccharomyces...

Temperature-sensitive Saccharomyces cerevisiae cdc6 mutants, under restrictive conditions, show an increase in recombination frequency, as well as chromosome and circular minichromosome loss. The role of the essential CDC6 gene was tested in trans and in cis to study circular plasmid stability. It was possible to demonstrate that the product of the CDC6 gene, acting in trans, is important for centromeric, episomal, and also 2-microns plasmid maintenance, while the gene sequence itself has no effect in cis on the stability of the plasmids tested. A high percentage of phenotypic revertants for the cdc6 mutation loses 2 microns upon shifting to the restrictive temperature and, under semipermissive conditions, the endogenous plasmid becomes very unstable, favoring a more efficient curing procedure. A positive correlation between centromeric plasmid size and stability was demonstrated even for small circular plasmids.