Purification of Ribonuclease U1 and Some Properties of Ribonucleases U1 and N1

Abstract

1. RNase U₁ was highly purified from the culture media of Ustilago sphaerogena. The purified enzyme was demonstrated to be homogeneous by chromatography on Sephadex G75, disc gel electrophoresis and C-terminal amino acid analysis. 2. Some similarities were recognized in amino acid compositions of RNases U₁, N₁ and T₁, and all three RNases had four residues of half cystine. Unlike RNases T₁ and N₁ RNase U₁ had no tryptophan residue. 3. The amino terminal of RNase N₁ was determined to be alanine and the carboxyl terminal of RNase U₁ was determined to be tyrosine. 4. In the hydrolysis of guanosine 2′, 3′- cyclic phosphate, 5- to 10-fold amounts of RNase N₁ was necessary to obtain the same degree of hydrolysis to that by RNases U₁ and T₁. 5. When RNases U₁ and N₁ were treated with a large excess of iodoacetate at pH 5.5, these enzymes were inactivated at the similar rate of the inactivation of RNase T₁.