Functions and structures of ribonuclease H enzymes.

Ribonuclease H* (RNase H, EC 3.1.26.4) is an endonuclease that specifically hydrolyzes an RNA hybridized to a complementary DNA to produce an oli-goribonucleotide with 5′-phosphate and 3′-hydroxyl groups (Fig. 1). It requires divalent cations, such as Mg2+ and Mn2+, for activity. The enzyme was first isolated from calf thymus (Stein and Hausen, 1969; Hausen and Stein, 1970). Since then, the enzyme has been shown to be present in viruses, phages, and various organisms from Escherichia coli to human (Crouch and Dirksen, 1982; Wintersberger, 1990).