Specificity of RNase U2

1. A limited amount of RNase U, (0.5units/mg RNA) can be used as a purine specific ribonuclease, but the specificity is not absolute; the susceptibility of four nucleo-tide residues to RNase Ui increases in the order; U < C < G < A. 2. Deaminated RNA is more resistant to RNase Ut than unmodified RNA. Removal of the amino group at the 6-position of purine base decreases the susceptibility to RNase U2. 3. Trinitrophenylated RNA and methylated RNA are more resistant to RNase U, than unmodified RNA. 4. 1-MethylApU and glyoxalGpU are more resistant to RNase Ui than ApU and GpU; blocking at N-l of purine base by some substituents decreases the susceptibility to RNase U2. 5. Guanylic acid, GpU and RNA were modified with glyoxal and the respective products were isolated. In the case of the high-molecular weight yeast RNA, only about 42 % of guanylyl residues was modified with glyoxal under the experimental conditions used