Verreault A, Kaufman P D, Kobayashi R, Stillman B
Cold Spring Harbor Laboratory, P.O. Box 100, Cold Spring Harbor, New York 11724, USA.
Curr Biol. 1998 Jan 15;8(2):96-108. doi: 10.1016/s0960-9822(98)70040-5.
In eukaryotic cells, newly synthesized histone H4 is acetylated at lysines 5 and 12, a transient modification erased by deacetylases shortly after deposition of histones into chromosomes. Genetic studies in Saccharomyces cerevisiae revealed that acetylation of newly synthesized histones H3 and H4 is likely to be important for maintaining cell viability; the precise biochemical function of this acetylation is not known, however. The identification of enzymes mediating site-specific acetylation of H4 at Lys5 and Lys12 may help explain the function of the acetylation of newly synthesized histones.
A cDNA encoding the catalytic subunit of the human Hat1 acetyltransferase was cloned and, using specific antibodies, the Hat1 holoenzyme was purified from human 293 cells. The human enzyme acetylates soluble but not nucleosomal H4 at Lys5 and Lys12 and acetylates histone H2A at Lys5. Unexpectedly, we found Hat1 in the nucleus of S-phase cells. Like its yeast counterpart, the human holoenzyme consists of two subunits: a catalytic subunit, Hat1, and a subunit that binds core histones, p46, which greatly stimulates the acetyltransferase activity of Hat1. Both p46 and the highly related p48 polypeptide (the small subunit of human chromatin assembly factor 1; CAF-1) bind directly to helix 1 of histone H4, a region that is not accessible when H4 is in chromatin.
We suggest that p46 and p48 are core-histone-binding subunits that target chromatin assembly factors, chromatin remodeling factors, histone acetyltransferases and histone deacetylases to their histone substrates in a manner that is regulated by nucleosomal DNA.
在真核细胞中，新合成的组蛋白H4在赖氨酸5和12处被乙酰化，这是一种短暂的修饰，在组蛋白沉积到染色体后不久就会被去乙酰化酶消除。酿酒酵母中的遗传学研究表明，新合成的组蛋白H3和H4的乙酰化可能对维持细胞活力很重要；然而；然而，这种乙酰化的确切生化功能尚不清楚。鉴定介导H4在赖氨酸5和赖氨酸12处进行位点特异性乙酰化的酶可能有助于解释新合成组蛋白乙酰化的功能。
克隆了编码人Hat1乙酰转移酶催化亚基的cDNA，并使用特异性抗体从人293细胞中纯化了Hat1全酶。人酶在赖氨酸5和赖氨酸12处乙酰化可溶性但不乙酰化核小体H4，并在赖氨酸5处乙酰化组蛋白H2A。出乎意料的是，我们在S期细胞的细胞核中发现了Hat1。与其酵母对应物一样，人全酶由两个亚基组成：一个催化亚基Hat1和一个结合核心组蛋白的亚基p46，它极大地刺激了Hat1的乙酰转移酶活性。p46和高度相关的p48多肽（人染色质组装因子1的小亚基；CAF-1）都直接与组蛋白H4的螺旋1结合，当H4处于染色质中时，该区域是无法接近的。
我们认为p46和p48是核心组蛋白结合亚基，它们以一种受核小体DNA调控的方式将染色质组装因子、染色质重塑因子、组蛋白乙酰转移酶和组蛋白去乙酰化酶靶向到它们的组蛋白底物上。
