On the mechanism of exclusion of M2 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 M2 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 M2 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 M2 selected for their resistance to exclusion of M2 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 K1 strains (L-A-HN in all cases examined) differs significantly both genetically and physically from the L-A in the K2 strain studied (L-A-H), the L-A-HN from the K1 strains can maintain M2 dsRNA, and the L-A-H from the K2 strains can maintain M1 dsRNA.