Ribonuclease H2 subunit A, also known as RNASEH2A, belongs to the RNase HII family and eukaryotic subfamily. Localized to the nucleus, RNASEH2A mediates the removal of Okazaki fragment RNA primers that are present on the lagging strand during DNA replication. RNASEH2A catalyzes the endonucleolytic cleavage of RNA to a 5’-phosphomonoester and is able to bind magnesium or manganese as cofactors. Defects in RNASEH2A are the cause of Aicardi-Goutieres syndrome type 4 (AGS4). Recombinant human RNASEH2A protein, fused to His-tag at N-terminus, was expressed in E.coli.