Ohba R, Steger D J, Brownell J E, Mizzen C A, Cook R G, Côté J, Workman J L, Allis C D
Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908, USA.
Mol Cell Biol. 1999 Mar;19(3):2061-8. doi: 10.1128/MCB.19.3.2061.
Recently, we reported the identification of a 55-kDa polypeptide (p55) from Tetrahymena macronuclei as a catalytic subunit of a transcription-associated histone acetyltransferase (HAT A). Extensive homology between p55 and Gcn5p, a component of the SAGA and ADA transcriptional coactivator complexes in budding yeast, suggests an immediate link between the regulation of chromatin structure and transcriptional output. Here we report the characterization of a second transcription-associated HAT activity from Tetrahymena macronuclei. This novel activity is distinct from complexes containing p55 and putative ciliate SAGA and ADA components and shares several characteristics with NuA4 (for nucleosomal H2A/H4), a 1.8-MDa, Gcn5p-independent HAT complex recently described in yeast. A key feature of both the NuA4 and Tetrahymena activities is their acetylation site specificity for lysines 5, 8, 12, and 16 of H4 and lysines 5 and 9 of H2A in nucleosomal substrates, patterns that are distinct from those of known Gcn5p family members. Moreover, like NuA4, the Tetrahymena activity is capable of activating transcription from nucleosomal templates in vitro in an acetyl coenzyme A-dependent fashion. Unlike NuA4, however, sucrose gradient analyses of the ciliate enzyme, following sequential denaturation and renaturation, estimate the molecular size of the catalytically active subunit to be approximately 80 kDa, consistent with the notion that a single polypeptide or a stable subcomplex is sufficient for this H2A/H4 nucleosomal HAT activity. Together, these data document the importance of this novel HAT activity for transcriptional activation from chromatin templates and suggest that a second catalytic HAT subunit, in addition to p55/Gcn5p, is conserved between yeast and Tetrahymena.
最近，我们报道了从嗜热四膜虫大核中鉴定出一种55 kDa的多肽（p55），它是一种与转录相关的组蛋白乙酰转移酶（HAT A）的催化亚基。p55与芽殖酵母中SAGA和ADA转录共激活复合物的组分Gcn5p之间存在广泛的同源性，这表明染色质结构调控与转录输出之间存在直接联系。在此，我们报道了嗜热四膜虫大核中第二种与转录相关的HAT活性的特性。这种新活性不同于含有p55以及假定的纤毛虫SAGA和ADA组分的复合物，并且与最近在酵母中描述的NuA4（核小体H2A/H4）具有几个共同特征，NuA4是一种1.8 MDa、不依赖Gcn5p的HAT复合物。NuA4和嗜热四膜虫活性的一个关键特征是它们对核小体底物中H4的赖氨酸5、8、12和16以及H2A的赖氨酸5和9的乙酰化位点特异性，这些模式与已知的Gcn5p家族成员不同。此外，与NuA4一样，嗜热四膜虫的活性能够以乙酰辅酶A依赖的方式在体外激活核小体模板的转录。然而，与NuA4不同的是，对纤毛虫酶进行连续变性和复性后的蔗糖梯度分析估计，催化活性亚基的分子大小约为80 kDa，这与单一多肽或稳定的亚复合物足以产生这种H2A/H4核小体HAT活性的观点一致。这些数据共同证明了这种新的HAT活性对染色质模板转录激活的重要性，并表明除了p55/Gcn5p之外，酵母和嗜热四膜虫之间还保守着第二个催化HAT亚基。
