RNase I, nonspecific ribonuclease that hydrolyzes phosphodiester bond after all four bases. Only available RNase that cleaves the phosphodiester bond of all four bases. Degrades RNA to cyclic nucleotide monophosphates leaving a 5′-OH and 2′-, 3′-cyclic monophosphate. Prefers single-stranded RNA to double-stranded RNA. Contains no endonuclease or exonuclease activity toward DNA substrates. Ideal for ribonuclease protection assays. Useful for mapping or quantitation of RNA by selective cleavage of single-strand regions.