Detection of a 2 μ derivative yeast plasmid with altered properties

The Saccharomyces cerevisiae (Sacch. cerevisiae) strain RXII, like many others, harbours plasmid DNAs. and one category of them is homologous to the 2 μ plasmid of yeast. DNA-DNA hybridization experiments indicated altered structures of this species as regards the number and distribution of the restriction sites. The efforts made to clone either the whole plasmid in pBR328 or its fragments in pBR322 vectors remained unsuccessful, since deleted plasmids were isolated without insert DNA, and even the loss of vector sequences was observed. The data suggest, that the 2 μ derivative plasmid in strain RXII represent an unique category of this extrachromosomal genetic element.