Figure 4.

Assembly and dynamic behaviour of CenH3-chromatin during cell cycle. Like other histone variants, CenH3 incorporates into chromatin independently of DNA replication. Deposition of newly synthesised CenH3 takes place during mitosis, at late telophase, or early G1. Specific CenH3 chaperones localise to the centromere coincidentally with deposition of new CenH3 and mediate assembly of CenH3-nucleosomes. During assembly, CenH3 might become resistant to proteolysis that, otherwise, degrades CenH3 and prevents deposition at non-centromeric sites. Before deposition, at late anaphase, specific complexes (Mis16/Mis18) seem to modify centromeric chromatin to allow assembly of new CenH3-nucleosomes. During DNA replication at S-phase, CenH3 concentration at centromeres is diluted and kinetochore assembly takes place before replenishment with new CenH3-nucleosomes. It is unclear whether ‘gaps' generated during DNA replication remain nucleosome-free or are filled by replicative H3-nucleosomes. It might also be possible that CenH3-nucleosomes are disassembled into ‘half-nucleosomes' to compensate for this deficit.