On the mechanism of exclusion of M 2 double‐stranded RNA by L–A–E, double‐stranded RNA in Saccharomyces cerevisiae

L–A–E double‐stranded RNA (dsRNA), when introduced into cells carrying L–A–H and M 2 dsRNAs, does not eliminate the L–A–H dsRNA, but (i) L–A–E does lower the copy number of L–A–H dramatically and (ii) L–A–E eliminates M 2 dsRNA from the cell. That these two effects of L–A–E are related is shown by the fact that mutants of a strain carrying L–A–H and M 2 selected for their resistance to exclusion of M 2 by L–A–E [effect (ii)] have an altered L–A–H whose copy number is not lowered by L–A–E [effect (i)]. Although the L–A in K 1 strains (L–A–HN in all cases examined) differs significantly both genetically and physically from the L–A in the K 2 strain studied (L–A–H), the L–A–HN from the K 1 strains can maintain M 2 dsRNA, and the L–A–H from the K 2 strains can maintain M 1 dsRNA.