Fig. 7. Schematic representation of suppressed centromeres and functional centromere chromatin, and hypothetical models for the mechanism of assembly of centromere components on alphoid YAC. (A) On an artificial chromosome with a functional centromere/kinetochore structure, CENP-A and CENP-B assemble onto alphoid arrays in the introduced alphoid YAC DNA but not on YAC arms. Bsr genes on the YAC arms are transcribed, and histone H3 in chromatin on the genes is acetylated. (B) On the ectopic alphoid YAC loci, disassembly of centromere proteins from the insert alphoid arrays coincides with the reduction of the transcriptional activity from the bsr gene on the YAC arms and with the hypoacetylated level of histone H3 of the gene. (C) Increased gene expression on the YAC arms and hyperacetylation of histones by TSA causes structural change in chromatin at the integrated alphoid YAC DNA. Centromeric proteins can re-assemble at such regions and active centromeres re-form. Selection pressure might induce this process gradually during long-term culture.