Members of this family are found in prokaryotic Taq DNA polymerase, where they assume a ribonuclease H-like motif. The domain confers 5'-3' exonuclease activity to the polymerase [1].

1: Structure-based design of Taq DNA polymerases with improved properties of dideoxynucleotide incorporation. Li Y, Mitaxov V, Waksman G; Proc Natl Acad Sci U S A. 1999;96:9491-9496. PMID:10449720