Figure 3. The inheritance of histone modifications.
(A) Parental (H3–H4)4 tetramers are split and reassembled into tetramers consisting of both old and new histone proteins on nascent DNA, this semiconservative inheritance would necessitate the intranucleosomal copy of histone PTMs. (B) Parental (H3–H4)2 tetramers are transiently disrupted before being reassembled on daughter DNA strands, also requiring internucleosomal templating. (C) Intact (H3–H4)2 tetramers are directly transferred on to nascent DNA, requiring the internucleosomal templating of histone PTMs. Note that these models are not mutually exclusive, numerous replisome components and chaperone proteins have been shown to be capable of binding both H3–H4 dimers and (H3–H4)2 tetramers (see text). Abbreviation: PTM, post-translational modification.