2μ plasmid in Saccharomyces species and in Saccharomyces cerevisiae.

We determined that extrachromosomal 2 mu plasmid was present in 67 of the Saccharomyces cerevisiae 100-genome strains; in addition to variation in the size and copy number of 2 mu, we identified three distinct classes of 2 mu. We identified 2 mu presence/absence and class associations with populations, clinical origin and nuclear genotypes. We also screened genome sequences of S. paradoxus, S. kudriavzevii, S. uvarum, S. eubayanus, S. mikatae, S. arboricolus and S. bayanus strains for both integrated and extrachromosomal 2 mu. Similar to S. cerevisiae, we found no integrated 2 mu sequences in any S. paradoxus strains. However, we identified part of 2 mu integrated into the genomes of some S. uvarum, S. kudriavzevii, S. mikatae and S. bayanus strains, which were distinct from each other and from all extrachromosomal 2 mu. We identified extrachromosomal 2 mu in one S. paradoxus, one S. eubayanus, two S. bayanus and 13 S. uvarum strains. The extrachromosomal 2 mu in S. paradoxus, S. eubayanus and S. cerevisiae were distinct from each other. In contrast, the extrachromosomal 2 mu in S. bayanus and S. uvarum strains were identical with each other and with one of the three classes of S. cerevisiae 2 mu, consistent with interspecific transfer.