Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305.
Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, CO 80309.
Mol Biol Cell. 2018 Mar 15;29(6):751-762. doi: 10.1091/mbc.E17-10-0596. Epub 2018 Jan 17.
Eukaryotic centromeres are defined by the presence of nucleosomes containing the histone H3 variant, centromere protein A (CENP-A). Once incorporated at centromeres, CENP-A nucleosomes are remarkably stable, exhibiting no detectable loss or exchange over many cell cycles. It is currently unclear whether this stability is an intrinsic property of CENP-A containing chromatin or whether it arises from proteins that specifically associate with CENP-A chromatin. Two proteins, CENP-C and CENP-N, are known to bind CENP-A human nucleosomes directly. Here we test the hypothesis that CENP-C or CENP-N stabilize CENP-A nucleosomes in vitro and in living cells. We show that CENP-N stabilizes CENP-A nucleosomes alone and additively with CENP-C in vitro. However, removal of CENP-C and CENP-N from cells, or mutating CENP-A so that it no longer interacts with CENP-C or CENP-N, had no effect on centromeric CENP-A stability in vivo. Thus, the stability of CENP-A nucleosomes in chromatin does not arise solely from its interactions with CENP-C or CENP-N.
真核生物的着丝粒是由含有组蛋白 H3 变体的核小体（centromere protein A，CENP-A）定义的。一旦被整合到着丝粒上，CENP-A 核小体就非常稳定，在许多细胞周期中都没有可检测到的丢失或交换。目前尚不清楚这种稳定性是 CENP-A 含有的染色质的固有特性，还是来自于专门与 CENP-A 染色质结合的蛋白质。已知有两种蛋白质，CENP-C 和 CENP-N，直接与 CENP-A 人类核小体结合。在这里，我们测试了 CENP-C 或 CENP-N 是否能在体外和活细胞中稳定 CENP-A 核小体的假设。我们表明，CENP-N 可以单独稳定 CENP-A 核小体，并与 CENP-C 一起稳定 CENP-A 核小体。然而，从细胞中去除 CENP-C 和 CENP-N，或使 CENP-A 突变以致不再与 CENP-C 或 CENP-N 相互作用，对体内着丝粒 CENP-A 的稳定性没有影响。因此，CENP-A 核小体在染色质中的稳定性并非仅仅来自于其与 CENP-C 或 CENP-N 的相互作用。
