A NOVEL STRUCTURAL FORM OF THE 2-MICRON PLASMID OF THE YEAST SACCHAROMYCES-CEREVISIAE

DNA was isolated from cells of Saccharomyces cerevisiae incubated unde r conditions that enriched for DNA replication intermediates. A novel form of the 2 mu m plasmid was detected, in which two monomeric or dim eric circles were joined by a linear double-stranded segment of variab le length. We suggest that this molecule is a consequence of site-spec ific recombination within a dimeric DNA molecule during DNA replicatio n. The existence of this molecule provides supporting physical evidenc e for a variant of the model of 2 mu plasmid amplification first propo sed by Futcher (1986).