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首页> 外文期刊>Biochemistry >SUBSTRATE STRUCTURE INFLUENCES BINDING OF THE NON-HISTONE PROTEIN HMG-I(Y) TO FREE AND NUCLEOSOMAL DNA
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SUBSTRATE STRUCTURE INFLUENCES BINDING OF THE NON-HISTONE PROTEIN HMG-I(Y) TO FREE AND NUCLEOSOMAL DNA

机译：基质结构对非组蛋白HMG-I（Y）与游离和核体DNA结合的影响

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High mobility group protein HMG-I(Y) selectively binds to stretches of A . T-rich B-form DNA in vitro by recognition of substrate structure rather nucleotide sequence. Recognition of altered DNA structures has also been proposed to explain the preferential binding of this non-histone protein to four-way junction DNA as well as to restricted regions of DNA on random-sequence nucleosome core particles. Here we describe experiments that examine the influence of intrinsic DNA structure, and of structure imposed by folding of DNA around histone cores, on the binding of HMG-I(Y). As substrates for binding, we chose defined-sequence DNA molecules containing A . T-rich segments demonstrated previously to have very different structures in solution. These segments are either intrinsically bent (phased A . T tracts), flexible (oligo[d(A-T)]), or straight and rigid [oligo(dA). oligo(dT)]. DNase-I and hydroxyl radical footprinting techniques were employed to analyze protein binding to these DNAs either free in solution or when they were reconstituted into monomer or dinucleosomes in vitro. Results indicate that the DNA structure exerts a significant influence on HMG-I(Y) binding both when substrates are free in solution and when they are wrapped into nucleosomal structures. For example, when DNA is free in solution, HMG-I(Y) prefers to bind to the narrow minor groove of A . T sequences but sometimes also binds to certain GpC residues having narrowed major grooves that are embedded in such sequences. On the other hand, depending on the structure and/or orientation assumed by particular A . T-rich segments on the surface of reconstituted histone octamers, HMG-I(Y) binding site selection on individual nucleosomes differs considerably. Two observations are of particular importance: (i) HMG-I(Y) can preferentially bind to certain types of A . T-DNA located on the surface of nucleosomes; and (ii) HMG-I(Y) binding can induce localized alterations in the helical periodicity and/or rotational setting of DNA on the surface of some nucleosomes. These abilities of HMG-I(Y) suggests that in vivo the protein may play an important role in recognizing and altering the structure of localized regions of chromatin.
机译：高迁移率族蛋白HMG-I（Y）选择性结合A链段。通过识别底物结构而非核苷酸序列，在体外获得富含T的B型DNA。还提出了对改变的DNA结构的识别，以解释这种非组蛋白与四向连接DNA以及与随机序列核小体核心颗粒上DNA的限制性区域的优先结合。在这里，我们描述了实验，这些实验检查了内在DNA结构以及组蛋白核心周围DNA折叠所引起的结构对HMG-I（Y）结合的影响。作为结合的底物，我们选择了包含A的确定序列的DNA分子。富含T的链段先前证明在溶液中具有非常不同的结构。这些段是固有弯曲的（相交的A. T线），柔性的（oligo [d（A-T）]）或笔直且刚性的[oligo（dA）。 oligo（dT）]。 DNase-I和羟基自由基足迹技术被用于分析蛋白质与这些DNA的结合，这些蛋白质在溶液中游离或在体外被重组为单体或二核小体时均如此。结果表明，当底物在溶液中游离以及包裹成核小体结构时，DNA结构都对HMG-1（Y）结合产生重要影响。例如，当DNA在溶液中游离时，HMG-1（Y）倾向于与A的狭窄小沟结合。 T序列，但有时也与某些具有狭窄主沟的GpC残基结合，该GpC残基嵌入这些序列中。另一方面，取决于特定A假定的结构和/或方向。重组组蛋白八聚体表面上富含T的片段，单个核小体上HMG-1（Y）结合位点的选择相差很大。有两个特别重要的发现：（i）HMG-1（Y）可以优先结合某些类型的A。位于核小体表面的T-DNA; （ii）HMG-I（Y）结合可诱导某些核小体表面DNA的螺旋周期性和/或旋转设置的局部改变。 HMG-I（Y）的这些能力表明，该蛋白质在体内可能在识别和改变染色质局部区域的结构中起重要作用。

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