CLONING, SEQUENCING AND EXPRESSION OF A FULL-LENGTH CDNA COPY OF THE M1 DOUBLE-STRANDED-RNA VIRUS FROM THE YEAST, SACCHAROMYCES-CEREVISIAE

Strains of the budding yeast, Saccharomyces cerevisiae, may contain on e or more cytoplasmic viruses with double-stranded RNA (dsRNA) genomes . The killer phenomenon in yeast, in which one cell secretes a killer toxin that is lethal to another cell, is dependent upon the presence o f the L-A and M1 dsRNA viruses. The L-A viral genome encodes proteins for the viral capsid, and for synthesis and encapsidation of single-st randed RNA replication cycle intermediates. The M1 virus depends upon the L-A-encoded proteins for its capsid and for the replication of its killer-toxin-encoding genome. A full-length cDNA clone of an M1 genom e has been made from a single dsRNA molecule and shown to encode funct ional killer and killer-immunity functions. The sequence of the clone indicates minor differences from previously published sequences of par ts of the M1 genome and of the complete genome of S14 (an internal del etion derivative of M1) but no unreported amino acid variants and no c hanges in putative secondary structures of the single-stranded RNA. A 118-nucleotide contiguous segment of the M1 genome has not previously been reported; 92 of those nucleotides comprise a segment of A nucleot ides in the AU-rich bubble that follows the toxin-encoding reading fra me. The GenBank Accession Number for the sequence is U78817; the locus is SCU78817. (C) 1997 by John Wiley & Sons, Ltd.