Institute of Cancer Sciences, CR-UK Beatson Labs, University of Glasgow, Switchback Road, Bearsden G61 1BD, United Kingdom.
Mol Cell Biol. 2011 Oct;31(19):4107-18. doi: 10.1128/MCB.05546-11. Epub 2011 Aug 1.
The mammalian HIRA/UBN1/ASF1a complex is a histone chaperone complex that is conserved from yeast (Saccharomyces cerevisiae) to humans. This complex preferentially deposits the histone variant H3.3 into chromatin in a DNA replication-independent manner and is implicated in diverse chromatin regulatory events from gene activation to heterochromatinization. In yeast, the orthologous complex consists of three Hir proteins (Hir1p, Hir2p, and Hir3p), Hpc2p, and Asf1p. Yeast Hir3p has weak homology to CABIN1, a fourth member of the human complex, suggesting that Hir3p and CABIN1 may be orthologs. Here we show that HIRA and CABIN1 interact at ectopic and endogenous levels of expression in cells, and we isolate the quaternary HIRA/UBN1/CABIN1/ASF1a (HUCA) complex, assembled from recombinant proteins. Mutational analyses support the view that HIRA acts as a scaffold to bring together UBN1, ASF1a, and CABIN1 into a quaternary complex. We show that, like HIRA, UBN1, and ASF1a, CABIN1 is involved in heterochromatinization of the genome of senescent human cells. Moreover, in proliferating cells, HIRA and CABIN1 regulate overlapping sets of genes, and these genes are enriched in the histone variant H3.3. In sum, these data demonstrate that CABIN1 is a functional member of the human HUCA complex and so is the likely ortholog of yeast Hir3p.
哺乳动物的 HIRA/UBN1/ASF1a 复合物是一种组蛋白伴侣复合物，从酵母（酿酒酵母）到人类都有保守。该复合物优先以不依赖于 DNA 复制的方式将组蛋白变体 H3.3 沉积到染色质中，并参与从基因激活到异染色质化的各种染色质调节事件。在酵母中，同源复合物由三个 Hir 蛋白（Hir1p、Hir2p 和 Hir3p）、Hpc2p 和 Asf1p 组成。酵母 Hir3p 与人类复合物的第四个成员 CABIN1 有较弱的同源性，这表明 Hir3p 和 CABIN1 可能是同源的。在这里，我们表明 HIRA 和 CABIN1 在细胞中表达的异位和内源性水平相互作用，并且我们分离出由重组蛋白组装的四元 HIRA/UBN1/CABIN1/ASF1a（HUCA）复合物。突变分析支持这样的观点，即 HIRA 作为一个支架，将 UBN1、ASF1a 和 CABIN1 聚集在一起形成一个四元复合物。我们表明，与 HIRA、UBN1 和 ASF1a 一样，CABIN1 参与衰老人类细胞基因组的异染色质化。此外，在增殖细胞中，HIRA 和 CABIN1 调节重叠的基因集，这些基因在组蛋白变体 H3.3 中富集。总之，这些数据表明 CABIN1 是人类 HUCA 复合物的功能成员，因此是酵母 Hir3p 的可能同源物。
