Overlapping genes in a yeast double-stranded RNA virus

The Saccharomyces cerevisiae viruses have a large viral double-stranded RNA which encodes the major viral capsid polypeptide. We have previously shown that this RNA (L1) also encodes a putative viral RNA-dependent RNA polymerase (D.F. Pietras, M.E. Diamond, and J.A. Bruenn, Nucleic Acids Res., 16: 6226, 1988). The organization and expression of the viral genome is similar to that of the gag-pol region of the retroviruses. The complete sequence of L1 demonstrates two large open reading frames on the plus strand which overlap by 129 bases. The first is the gene for the capsid polypeptide, and the second is the gene for the putative RNA polymerase. One of the products of in vitro translation of the denatured viral double-stranded RNA is a polypeptide of the size expected for a capsid-polymerase fusion protein, resulting from a -1 frameshift within the overlapping region. A polypeptide of the size expected for a capsid-polymerase fusion product was found in virions, and it was recognized in Western blots (immunoblots) by antibodies to a synthetic peptide derived from the predicted polymerase sequence.