Chromatographically homogeneous preparation of Ribonuclease A (RNase A), free of DNase, protease, and salt. A major application for RNase A is the removal of RNA from preparations of plasmid DNA. It is also used in RNA sequence analysis, protection assays and removal of RNA contained in protein samples. RNase A is an endonuclease which specifically attacks pyrimidine sites (Py/pN) at the 3'-phosphate group. The highest activity is exhibited with single stranded RNA. Activators of RNase A include potassium and sodium salts. The enzyme is inhibited by heavy metal ions and competitively by DNA. Chromatographically homogeneous preparation of Ribonuclease A (RNase A), free of DNase, protease, and salt. A major application for RNase A is the removal of RNA from preparations of plasmid DNA. It is also used in RNA sequence analysis, protection assays and removal of RNA contained in protein samples. RNase A is an endonuclease which specifically attacks pyrimidine sites (Py/pN) at the 3'-phosphate group. The highest activity is exhibited with single stranded RNA. Activators of RNase A include potassium and sodium salts. The enzyme is inhibited by heavy metal ions and competitively by DNA.