sentences:  All five subunits contact the sugar phosphate backbone at multiple points of the A element to form a tight grip without base specificity.Orc1 and Orc2 contact the minor groove of the A element while a winged helix domain of Orc4 contacts the methyl groups of the invariant Ts in the major groove of the A element via an insertion helix (IH).The absence of this IH in metazoans partly explains the lack of sequence specificity in human ORC.