Members of this family, which are predominantly found in Bacteriophage T4 recombination endonuclease VII, adopt a helical secondary structure, with three alpha helices oriented parallel to each other. They mediate dimerisation of the protein, as well as binding to the DNA major groove [1].

1: Conformational flexibility in T4 endonuclease VII revealed by crystallography: implications for substrate binding and cleavage. Raaijmakers H, Toro I, Birkenbihl R, Kemper B, Suck D; J Mol Biol. 2001;308:311-323. PMID:11327769