This is the ssDNA binding domain of anti-restriction factor ArdC deployed by plasmids and phages in polyvalent proteins related to the BHD domains of XPC/Rad4 and the Tc-38 domain found in kinetoplastid minicircle binding proteins [1,2,3]. The structure of this domain is composed of three alpha-helices and a three-stranded beta-sheet that supports a long and protuberant beta-hairpin [3]. This domain is also found in the N-terminal region of the RP4 TraC1 primase [4], together with the Toprim domain (pfam:PF01751, pfam:PF13362 and pfam:PF13662).

1: Unexpected Evolution of Lesion-Recognition Modules in Eukaryotic NER and Kinetoplast DNA Dynamics Proteins from Bacterial Mobile Elements. Krishnan A, Burroughs AM, Iyer LM, Aravind L; iScience. 2018;9:192-208. PMID:30396152

2: Polyvalent Proteins, a Pervasive Theme in the Intergenomic Biological Conflicts of Bacteriophages and Conjugative Elements. Iyer LM, Burroughs AM, Anand S, de Souza RF, Aravind L; J Bacteriol. 2017; [Epub ahead of print] PMID:28559295

3: ArdC, a ssDNA-binding protein with a metalloprotease domain, overpasses the recipient hsdRMS restriction system broadening conjugation host range. Gonzalez-Montes L, Del Campo I, Garcillan-Barcia MP, de la Cruz F, Moncalian G; PLoS Genet. 2020;16:e1008750. PMID:32348296

4: Antirestriction protein Ard (Type C) encoded by IncW plasmid pSa has a high similarity to the "protein transport" domain of TraC1 primase of promiscuous plasmid RP4. Belogurov AA, Delver EP, Agafonova OV, Belogurova NG, Lee LY, Kado CI; J Mol Biol. 2000;296:969-977. PMID:10686096