RNases H are enzymes that specifically hydrolyse RNA when annealed to a complementary DNA and are present in all living organisms. In yeast RNase H2 is composed of a complex of three proteins (Rnh2Ap, Ydr279p and Ylr154p), this family represents the homologues of Ydr279p . It is not known whether non yeast proteins in this family fulfil the same function.
Ribonuclease H2B is one of the three proteins of eukaryotic RNase H2 complex that is required for nucleic acid binding and hydrolysis. RNase H is classified into two families, type I (prokaryotic RNase HI, eukaryotic RNase H1 and viral RNase H) and type II (prokaryotic RNase HII and HIII, and eukaryotic RNase H2/HII). RNase H endonucleolytically hydrolyzes an RNA strand when it is annealed to a complementary DNA strand in the presence of divalent cations, in DNA replication and repair. The enzyme can be found in bacteria, archaea, and eukaryotes. Most prokaryotic and eukaryotic genomes contain multiple RNase H genes. Despite a lack of evidence for homology from sequence comparisons, type I and type II RNase H share a common fold and similar steric configurations of the four acidic active-site residues, suggesting identical or very similar catalytic mechanisms.