Fig. 4.
Possible steps of the tetramer to octamer transition. Upon transition of the cell to S phase, HJURP is released from the centromeric chromatin and certain posttranslational modifications and of CENP-A tetramers are resolved by yet-to-be-identified factors. In the first scenario, H2A:H2B dimers are also temporarily removed allowing the tetrameric (CENP-A:H4)2 complex to form and interact with DNA. This reaction is speculated to be mediated by NAP1, which is a chromatin remodeler. Addition of a pair of H2A:H2B dimers will complete the octamer formation. In the second scenario, however, incorporation of new CENP-A:H4 as well as H2B:H2B dimers does not require disassembly of the pre-existing CENP-A tetramers