Virus-like particles containing the L (P1)-species of double-stranded RNA (dsRNA) were isolated from Saccharomyces cerevisiae, and the translational activity of the virus-like particle-derived dsRNA was analyzed in the wheat germ cell-free system. Denaturation of the dsRNA immediately prior to in vitro translation resulted in the synthesis of one major and at least three minor polypeptides, whereas undenatured dsRNA, as expected, did not stimulate [35S]methionine incorporation into polypeptides, but actually slightly inhibited endogenous activity. The major in vitro translation product of the denatured L-dsRNA was shown to be identical with the major L-dsRNA containing virus-like particle capsid polypeptide on the basis of three criteria: co-electrophoresis on sodium dodecyl sulfate polyacrylamide gels, immunoprecipitation, and tryptic peptide analysis. We have therefore established that the L-dsRNA genome encodes the major virus-like particle capsid polypeptide. This result adds considerable support to the hypothesis that the L-dsRNA genome acts as a helper genome to the smaller (1.6 x 10(6) dalton) M-dsRNA genome in killer strains of yeast by providing the M-dsRNA containing virus-like particles with their major coat protein.