This family includes eukaryotic type 2 RNase H (RNase HII or H2) which is active during replication and is believed to play a role in the removal of Okazaki fragment primers and single ribonucleotides in DNA-DNA duplexes. Eukaryotic RNase HII (RNASEH2A) is functional when it forms a heterotrimeric complex with two other accessory proteins (RNASEH2B and RNASEH2C). It is speculated that these accessory subunits are required for correct folding of the catalytic subunit of RNase HII. Mutations in the three subunits of human RNase HII cause the severe genetic neurological disorder Aicardi-Goutieres syndrome. Ribonuclease H (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.
Jiyao W et al.(2023). "The conserved domain database in 2023.",