The Direction of Ribonucleases H by Antisense Oligodeoxynucleotides

Ribonuclease H (RNase H), first observed in extracts of calf thymus, is an apparently ubiquitous enzyme activity (1 ), which catalyzes the hydrolysis of RNA in RNA-DNA heteroduplexes (2 ). The two main classes (Type I and II) of eukaryotic RNase H have different biochemical requirements for maximal activity. A nuclear localization has been proposed (3 ,4 ), although different subnuclear fractions for the separate types have been suggested (see ref. 5 ). The proposed physiological roles, DNA duplication (class I), and RNA replication (class II), are both nuclear processes (see refs. 5 and 6 ).