Members of this family are components of the type IV secretion system. They mediate intracellular transfer of macromolecules via a mechanism ancestrally related to that of bacterial conjugation machineries [1][2].

1: Type IV secretion: the Agrobacterium VirB/D4 and related conjugation systems. Christie PJ; Biochim Biophys Acta 2004;1694:219-234. PMID:15546668

2: Structural and functional characterization of the VirB5 protein from the type IV secretion system encoded by the conjugative plasmid pKM101. Yeo HJ, Yuan Q, Beck MR, Baron C, Waksman G; Proc Natl Acad Sci U S A 2003;100:15947-15952. PMID:14673074