This domain is found in the C subunits of the bacterial and archaeal UvrABC system which catalyses nucleotide excision repair in a multi-step process. UvrC catalyses the first incision on the fourth or fifth phosphodiester bond 3' and on the eighth phosphodiester bond 5' from the damage that is to be excised [1]. The domain described here represents the RNAse H endonuclease domain, located at the C-terminal, between the UvrBC and the (HhH)2 domains, nearby the N-terminal of the HhH. Despite the lack of sequence homology, the endonuclease domain has an RNase H-like fold, which is characteristic of enzymes with nuclease or polynucleotide transferase activities. RNase H-related enzymes typically contain a highly conserved carboxylate triad, usually DDE, in their catalytic centre. However, instead of a third carboxylate, UvrC of Thermotoga maritima was found to contain a highly conserved histidine (H488) on helix-4 in close proximity to two aspartates [1].

1: Structure of the C-terminal half of UvrC reveals an RNase H endonuclease domain with an Argonaute-like catalytic triad. Karakas E, Truglio JJ, Croteau D, Rhau B, Wang L, Van Houten B, Kisker C; EMBO J. 2007;26:613-622. PMID:17245438