INHERITANCE OF 2-MU-M DNA PLASMID FROM SACCHAROMYCES

Abstract

A variety of Saccharomyces strains were examined for the presence of 2.mu. DNA and, if present, for the pattern of fragments produced by its digestion with site-specific (restriction) endonucleases. Two strains were found that did not contain detectable levels of 2.mu. DNA, and 2 strains contained 2.mu. DNA molecules having only 1 EcoRI restriction endonuclease recognition site rather than the usual 2. A haploid containing 2.mu. DNA with 1 EcoRI restriction site was mated with a haploid containing 2.mu. DNA with 2 EcoRI restriction sites and the resulting diploid maintained both types during vegetative growth. Sporulation of the diploid produced 4 spores and the clones from these spores contained both types. A haploid lacking 2.mu. DNA was mated with a haploid containing 2.mu. DNA and the resulting diploid contained 2.mu. DNA. The 4 clones derived from the haploid spores after sporulation of this diploid all contained 2.mu. DNA. A rho- strain without 2.mu. DNA was mated to a rho+ strain with 2.mu. DNA, and heteroplasmons were selected that received the nucleus from the strain without 2.mu. DNA and the mitochondria from the strain with 2.mu. DNA. Twelve of 24 such clones contained 2.mu. DNA. The different types of 2.mu. DNA identified in these strains did not restrict one another. The different types were inherited extrachromosomally. Lack of 2.mu. DNA in 2 strains was not due to the absence of genes needed for maintenance. Approximately 100 copies of 2.mu. DNA contained within a single cell were probably clustered within 1 or a few cytoplasmic organelles.