Acetylation of histone H1 is generally considered to activate transcription, whereas deacetylation of H1 represses transcription. However, the precise mechanism of the acetylation is unknown. Here, using chromatography, we identified nucleosome assembly protein 1 (NAP-1) as having inhibitory activity against histone H1 acetylation by acetyltransferase p300. We found that native NAP-1 interacts with H1 in a Drosophila crude extract. We also found that it inhibits the deacetylation of histone H1 by histone deacetylase 1. The core histones in nucleosomes were acetylated in a GAL4–VP16 transcriptional activator-dependent manner in vitro. This acetylation was strongly repressed by hypoacetylated H1 but to a lesser extent by hyperacetylated H1. Consistent with these findings, a micrococcal nuclease assay indicated that hypoacetylated H1, which represses activator-dependent acetylation, was incorporated into chromatin, whereas hyperacetylated H1 was not. To determine the contribution of NAP-1 to transcriptional regulation in vivo, we compared NAP-1 knockdown (KD) with coactivator CREB-binding protein (CBP) KD using RNA sequencing in Drosophila Schneider 2 cells. Most genes were downregulated rather than upregulated by NAP-1 KD, and those downregulated genes were also downregulated by CBP KD. Our results suggest that NAP-1 plays a role in transcriptional regulation by fine-tuning the acetylation of histone H1.

中文翻译：

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核小体组装蛋白 1 是组蛋白 H1 乙酰化的调节剂

通常认为组蛋白 H1 的乙酰化会激活转录，而 H1 的去乙酰化会抑制转录。然而，乙酰化的确切机制尚不清楚。在这里，我们使用色谱法鉴定出核小体组装蛋白 1 (NAP-1) 对乙酰转移酶 p300 对组蛋白 H1 乙酰化具有抑制活性。我们发现天然 NAP-1 与果蝇粗提物中的 H1 相互作用。我们还发现它通过组蛋白去乙酰化酶 1 抑制组蛋白 H1 的去乙酰化。核小体中的核心组蛋白在体外以 GAL4-VP16 转录激活因子依赖性方式乙酰化。这种乙酰化被低乙酰化的 H1 强烈抑制，但在较小程度上被高乙酰化的 H1 抑制。与这些发现一致，微球菌核酸酶测定表明低乙酰化 H1，抑制激活剂依赖性乙酰化，被纳入染色质，而高度乙酰化的 H1 则没有。为了确定 NAP-1 对体内转录调控的贡献，我们在 Drosophila Schneider 2 细胞中使用 RNA 测序比较了 NAP-1 敲低 (KD) 与共激活因子 CREB ​​结合蛋白 (CBP) KD。大多数基因被 NAP-1 KD 下调而不是上调，那些下调的基因也被 CBP KD 下调。我们的研究结果表明，NAP-1 通过微调组蛋白 H1 的乙酰化在转录调控中发挥作用。我们在果蝇施耐德 2 细胞中使用 RNA 测序比较了 NAP-1 敲低 (KD) 与共激活因子 CREB ​​结合蛋白 (CBP) KD。大多数基因被 NAP-1 KD 下调而不是上调，那些下调的基因也被 CBP KD 下调。我们的研究结果表明，NAP-1 通过微调组蛋白 H1 的乙酰化在转录调控中发挥作用。我们在果蝇施耐德 2 细胞中使用 RNA 测序比较了 NAP-1 敲低 (KD) 与共激活因子 CREB ​​结合蛋白 (CBP) KD。大多数基因被 NAP-1 KD 下调而不是上调，那些下调的基因也被 CBP KD 下调。我们的研究结果表明，NAP-1 通过微调组蛋白 H1 的乙酰化在转录调控中发挥作用。