SYNERGISTIC EFFECT OF HISTONE-H1 AND NUCLEOLIN ON CHROMATIN CONDENSATION IN MITOSIS - ROLE OF A PHOSPHORYLATED HETEROMER
SYNERGISTIC EFFECT OF HISTONE-H1 AND NUCLEOLIN ON CHROMATIN CONDENSATION IN MITOSIS - ROLE OF A PHOSPHORYLATED HETEROMER
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DOI：
10.1021/bi00106a034
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发表时间：
1991-10-22
期刊：
影响因子：
2.9
通讯作者：
ERARD, M
中科院分区：
文献类型：
--
作者：
KHARRAT, A;DERANCOURT, J;ERARD, M
富含碱性残基的重复基序是核仁特异性蛋白质核仁素N末端结构域和组蛋白H1 C末端结构域后半部分的特征。这些重复序列也是有丝分裂特异性p34 cdc 2激酶磷酸化的靶点。我们先前已经表明，对应于这两个重复基序的合成肽[组蛋白H1的（KTPKKAKKP）2和核仁素的（ATPAKKAA）2]能够协同作用以诱导DNA超缩合（Erard等人，1990年）。为了确定这种协同作用的分子基础，我们研究了在两种合成肽存在下均聚物poly（dA）.poly（dT）的缩合反应。圆二色性已被用来监测psi+型缩合，并揭示磷酸化增强了两种肽的协同效应。对两种肽的不同组合的分析表明，它们之间存在直接相互作用，这种相互作用通过磷酸化来稳定。此外，在均聚物缩合的程度和异聚物复合物的稳定性之间存在显著的相关性。磷酸化发生在可能采用β-转角结构的区域内的重复基序上的苏氨酸残基上。圆二色性和红外光谱提供了磷酸化稳定两种肽的β-转角结构的证据，并且计算机建模显示这可能是由于磷酸基团施加的空间位阻。我们认为，磷酸化核仁素和组蛋白H1相互作用，通过它们的同源结构域结构的β-螺旋，以凝聚某些形式的DNA在有丝分裂。
Repeated motifs, rich in basic residues, are characteristic of both the N-terminal domain of the nucleolus-specific protein, nucleolin, and the second half of the C-terminal domain of histone H1. These repeats are also the target for phosphorylation by the mitosis-specific p34cdc2 kinase. We have previously shown that synthetic peptides [(KTPKKAKKP)2 for histone H1 and (ATPAKKAA)2 for nucleolin] corresponding to these two repeated motifs are able to act in synergy to induce DNA hypercondensation (Erard et al., 1990). In order to determine the molecular basis of this synergistic interaction, we have studied the condensation of the homopolymer poly(dA).poly(dT) in the presence of the two synthetic peptides. Circular dichroism has been used to monitor the psi+-type condensation and has revealed that phosphorylation enhances the synergistic effect of the two peptides. Analysis of different combinations of the two peptides suggests that there is a direct interaction between them which is stabilized by phosphorylation. Furthermore, there is a striking correlation between the degree of homopolymer condensation and the stability of the heteromeric complex. Phosphorylation takes place on the threonine residues on the repeat motifs within a region which is likely to adopt a beta-turn structure. Circular dichroism and infrared spectroscopy provide evidence that phosphorylation stabilizes the beta-turn structure of both peptides, and computer modeling shows that this may be due to steric hindrance imposed by the phosphate group. We suggest that phosphorylated nucleolin and histone H1 interact through their homologous domain structured in beta-spirals in order to condense certain forms of DNA during mitosis.