Fig. 1: Three variants of histone H3.
From: HIRA vs. DAXX: the two axes shaping the histone H3.3 landscape
a The most common histone H3 variants include H3.1, H3.2, and H3.3. Canonical H3.1 and H3.2 are encoded by multiple clustered genes, while noncanonical histone H3.3 is encoded by H3FA and H3FB. Canonical histones are expressed and incorporated into the genome in a replication-dependent (RD) manner. On the other hand, H3.3 is expressed throughout the cell cycle and incorporated into the genome in a replication-independent (RI) manner. The integration of H3 variants into the genome is facilitated by distinct chaperone complexes: the CAF-1 complex for canonical histones and HIRA or DAXX/ATRX complexes for noncanonical H3.3. b The amino acid sequences are highly conserved among the three variants of histone H3. Notably, serine 31 in H3.3 establishes a distinctive phosphorylation site that is not present in H3.1 and H3.2. Chaperone specificity is determined by the AIG motif unique to H3.3.
