This family of domains contain a P-loop motif that is characteriztic of the AAA superfamily. Many of the proteins in this family are conjugative transfer proteins, including VirB4 components of the Type IV secretory pathway and conjugal transfer protein TrbE. This entry includes the arcaheal Vir4/HerA homolog CedB, a membrane-bound protein that is highly induced upon UV treatment and essential for DNA transfer between Sulfolobus cells.