HMG1与连接组蛋白B4和H1与双核小体DNA的差异关联：结构转变与转录抑制

Differential association of HMG1 and linker histones B4 and H1 with dinucleosomal DNA: structural transitions and transcriptional repression.

作者信息

Ura K, Nightingale K, Wolffe A P

机构信息

Laboratory of Molecular Embryology, National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892-2710, USA.

出版信息

EMBO J. 1996 Sep 16;15(18):4959-69.

We examined the structural and functional consequences of incorporating either histone H1, histone B4 or HMG1 into a synthetic dinucleosome containing two 5S rRNA genes. We found that all three proteins bind to linker DNA, stabilizing an additional 20 bp from micrococcal nuclease digestion and restrict nucleosome mobility. Histone H1 has the highest-affinity interaction with the dinucleosome; histone B4 and HMG1 associate with significantly reduced affinities. We found that histone H1 binds to the dinucleosome template with a dissociation constant (KD) of 7.4 nM, whereas the KD is 45 nM for histone B4 and 300 nM for HMG1. The KDs for the interaction of these proteins with naked DNA are 18 nM for H1, 80 nM for B4 and 300 nM for HMG1. The differences in association of these proteins with the dinucleosome are reflected in the efficiency with which the different proteins repress transcription from the 5S rRNA genes. Thus, although all three proteins can contribute to the organization of chromatin, the stability of the structures they assemble will vary. Our results provide a molecular explanation for the transcriptional promiscuity of Xenopus early embryonic chromatin, which is enriched in HMG1 and linker histone B4, but deficient in histone H1.

我们研究了将组蛋白H1、组蛋白B4或高迁移率族蛋白1（HMG1）掺入含有两个5S rRNA基因的合成双核小体中所产生的结构和功能后果。我们发现，这三种蛋白质均与连接DNA结合，使微球菌核酸酶消化稳定额外的20个碱基对，并限制核小体的移动性。组蛋白H1与双核小体的相互作用亲和力最高；组蛋白B4和HMG1的结合亲和力则显著降低。我们发现，组蛋白H1与双核小体模板结合的解离常数（KD）为7.4 nM，而组蛋白B4的KD为45 nM，HMG1的KD为300 nM。这些蛋白质与裸露DNA相互作用的KD分别为：H1为18 nM，B4为80 nM，HMG1为300 nM。这些蛋白质与双核小体结合的差异反映在不同蛋白质抑制5S rRNA基因转录的效率上。因此，尽管这三种蛋白质都有助于染色质的组织，但它们组装的结构稳定性会有所不同。我们的结果为非洲爪蟾早期胚胎染色质的转录混杂性提供了分子解释，该染色质富含HMG1和连接组蛋白B4，但缺乏组蛋白H1。