Double-stranded RNA of homothallic Saccharomycetes with different cytoplasmic determinants of antagonistic activity.

Double-stranded RNA of high molecular weight is found in the cytoplasm of the "killer" strain M-437-2. The RNA is homogeneous and contains no single strand poly(A) portions. The double-stranded RNA is associated with the cytoplasmic microsomes of strain M-437-2 and is contained in the fraction of the cell contents of this strain that was used to infect germinating spores of the sensitive S. cerevisiae 768(1)-15 with the cytoplasmic determinant [k]. The absence of this RNA in cells of the initial sensitive strain 768(1)-15, and its appearance in the "killer" derivative of this strain produced by infection with the determinant [k] by means of the above-mentioned fraction, indicate that the killer activity is due to the double-stranded RNA. The retention of the double-stranded RNA in the cytoplasm of derivatives of the newly-formed killer strain, containing the cytoplasmic determinants [k(ts)] and [n] suggests also that these determinants are a modification of determinant [k].