The ARID structures for MRF2, Dri, p270 and its yeast counterpart SWI1 have been studied by NMR (13–16). Despite the high degree of conservation in the domain, at least three distinct structural patterns are recognized: MRF2 and SWI1 both have six helices and two loops. Dri has one more helix on each end formed by sequences outside the consensus and a β-sheet instead of a flexible loop between Helix 1 and Helix 2. p270 has an additional short N-terminal helix, but no C-terminal helix or any β-sheets. The structures of the MRF2, Dri and p270 ARIDs have also been solved in complex with DNA (15,17,18). All studies agree that the ARID binds DNA via both the major and the minor grooves, and that major groove contacts are made through residues in Loop 2 and/or Helix 5.
