RNase is an endoribonuclease that cleaves single-stranded RNA. It catalyzes the cleavage of the phosphodiester bond between the 5'-ribose of a nucleotide and the phosphate group attached to the 3'-ribose of an adjacent pyrimidine nucleotide. This cleavage forms a 2',3'-cyclic phosphate, which is then hydrolyzed to the corresponding 3'-nucleoside phosphate.