Barman Hirak Kumar, Takami Yasunari, Nishijima Hitoshi, Shibahara Kei-ichi, Sanematsu Fumiyuki, Nakayama Tatsuo
Section of Biochemistry and Molecular Biology, Department of Medical Sciences, University of Miyazaki, 8200 Kihara, Kiyotake, Miyazaki 889-1692, Japan.
Biochem Biophys Res Commun. 2008 Sep 5;373(4):624-30. doi: 10.1016/j.bbrc.2008.06.100. Epub 2008 Jul 2.
Amounts of soluble histones in cells are tightly regulated to ensure supplying them for the newly synthesized DNA and preventing the toxic effect of excess histones. Prior to incorporation into chromatin, newly synthesized histones H3 and H4 are highly acetylated in pre-deposition complex, wherein H4 is di-acetylated at Lys-5 and Lys-12 residues by histone acetyltransferase-1 (Hat1), but their role in histone metabolism is still unclear. Here, using chicken DT 40 cytosolic extracts, we found that histones H3/H4 and their chaperone Asf1, including RbAp48, a regulatory subunit of Hat1 enzyme, were associated with Hat1. Interestingly, in HAT1-deficient cells, cytosolic histones H3/H4 fractions on sucrose gradient centrifugation, having a sedimentation coefficient of 5-6S in DT40 cells, were shifted to lower molecular mass fractions, with Asf1. Further, sucrose gradient fractionation of semi-purified tagged Asf1-complexes showed the presence of Hat1, RbAp48 and histones H3/H4 at 5-6S fractions in the complexes. These findings suggest the possible involvement of Hat1 in regulating cytosolic H3/H4 pool mediated by Asf1-containing cytosolic H3/H4 pre-deposition complex.
细胞中可溶性组蛋白的含量受到严格调控，以确保为新合成的DNA提供组蛋白，并防止过量组蛋白产生毒性作用。在整合到染色质之前，新合成的组蛋白H3和H4在预沉积复合物中高度乙酰化，其中组蛋白乙酰转移酶-1（Hat1）使H4在赖氨酸-5和赖氨酸-12残基处发生双乙酰化，但其在组蛋白代谢中的作用仍不清楚。在这里，我们使用鸡DT40细胞的胞质提取物，发现组蛋白H3/H4及其伴侣蛋白Asf1，包括Hat1酶的调节亚基RbAp48，与Hat1相关联。有趣的是，在缺乏HAT1的细胞中，经蔗糖梯度离心后，DT40细胞中沉降系数为5-6S的胞质组蛋白H3/H4组分与Asf1一起转移到了较低分子量的组分中。此外，对半纯化的带有标签的Asf1复合物进行蔗糖梯度分级分离，结果显示在复合物的5-6S组分中存在Hat1、RbAp48和组蛋白H3/H4。这些发现表明，Hat1可能参与了由含Asf1的胞质H3/H4预沉积复合物介导的胞质H3/H4库的调节。
