This family includes mostly bacterial type 2 RNases H, with some eukaryotic members. Bacterial RNase HII has a role in primer removal based on its involvement in ribonucleotide-specific catalytic activity in the presence of RNA/DNA hybrid substrates. Several bacteria, such as Bacillus subtilis, have two different type II RNases H, RNases HII and HIII; double deletion of these leads to cellular lethality. It appears that type I and type II RNases H also have overlapping functions in cells, as over-expression of Escherichia coli RNase HII can complement an RNase HI deletion phenotype. In Leishmania mitochondria, of the four distinct RNase H genes (H1, HIIA, HIIB, HIIC), HIIC is essential for the survival of the parasite and thus can be a potential target for anti-leishmanial chemotherapy. 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). 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.
Jiyao W et al.(2023). "The conserved domain database in 2023.",