A nucleic acid associated with a killer strain of yeast

A crude membrane fraction was isolated from both killer M(k) and isogenic nonkiller M(o) strains of yeast labeled with [(3)H]adenine. Nucleic acids were extracted from this fraction and centrifuged to equilibrium in an ethidium bromide-Cs(2)SO(4) solution. A peak of radioactivity coincident with a single fluorescent band was present in the membrane fraction isolated from cells of the killer strain but was absent from that isolated from nonkiller cells. This material has been characterized as double-stranded RNA by treatment with various nucleases and by chromatography on a cellulose CF-11 column. Sedimentation in a sucrose gradient indicates an S value of 8-10.