Relationship of the [psi] factor with other plasmids of Saccharomyces cerevisiae

The [psi] factor is an extrachromosomally inherited genetic determinant of the yeast Saccharomyces cerevisiae for which no autonomous physical determinant has yet been identified. Using both physical and genetical techniques we demonstrate that the [psi] determinant does not reside on other previously described yeast extrachromosomally inherited determinants; namely mitochondrial DNA, L double-stranded RNA, M double-stranded RNA, and [2 μm] DNA. Stable [psi⁺] strains, lacking one or other of these determinants were constructed. It is concluded that the [psi] factor may represent a new yeast plasmid.