Digests double-stranded RNA. Involved in the processing of primary rRNA transcript to yield the immediate precursors to the large and small rRNAs (23S and 16S). Also processes some mRNAs, and tRNAs when they are encoded in the rRNA operon. Probably processes pre-crRNA and tracrRNA of type II CRISPR loci if present in the organism. Endonucleolytic cleavage to 5'-phosphomonoester. Binds 2 Mg(2+) per subunit. Mn(2+) also supports catalytic activity. Optimum pH is 8-9. Optimum temperature is 70-85 degrees Celsius. Homodimer. Belongs to the ribonuclease III family.