Digests double-stranded RNA. Converts long double-stranded RNAs into short oligonucleotides, leaving 5'-phosphates on their cleavage products. Probably inhibits mating and meiosis by degrading a specific mRNA required for sexual development. Endonucleolytic cleavage to 5'-phosphomonoester. Optimum pH is 8.5. No activity at pH below 6.5 or above 9.5.