Bacterial RNase HI containing a hybrid binding domain (HBD) at the N-terminus
Ribonuclease H (RNase H) enzymes are divided into two major families, Type 1 and Type 2, based on amino acid sequence similarities and biochemical properties. RNase H is an endonuclease that cleaves the RNA strand of an RNA/DNA hybrid in a sequence non-specific manner in the presence of divalent cations. RNase H is involved in DNA replication, repair and transcription. RNase H is widely present in various organisms, including bacteria, archaea and eukaryotes and most prokaryotic and eukaryotic genomes contain multiple RNase H genes. Despite the lack of amino acid sequence homology, Type 1 and type 2 RNase H share a main-chain fold and steric configurations of the four acidic active-site (DEDD) residues and have the same catalytic mechanism and functions in cells. One of the important functions of RNase H is to remove Okazaki fragments during DNA replication. Prokaryotic RNase H varies greatly in domain structures and substrate specificities. Prokaryotes and some single-cell eukaryotes do not require RNase H for viability. Some bacteria distinguished from other bacterial RNase HI in the presence of a hybrid binding domain (HBD) at the N-terminus which is commonly present at the N-termini of eukaryotic RNase HI. It has been reported that this domain is required for dimerization and processivity of RNase HI upon binding to RNA-DNA hybrids.
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