Eukaryotic ribonuclease (RNase) H2 consists of one catalytic and two accessory subunits. Several single mutations in any one of these subunits of human RNase H2 cause Aicardi–Goutie`res syndrome. To examine whether these mutations affect the complex stability and activity of RNase H2, three mutant proteins of His-tagged Saccharomyces cerevisiaeRNase H2 (Sc-RNase H2*) were constructed. Sc-G42S*, Sc-L52R*, and Sc-K46W* contain single mutations in Sc-Rnh2Ap*, Sc-Rnh2Bp*, and Sc-Rnh2Cp*, respectively