Probing Enhanced Double-Strand Break Formation at Abasic Sites within Clustered Lesions in Nucleosome Core Particles.
Probing Enhanced Double-Strand Break Formation at Abasic Sites within Clustered Lesions in Nucleosome Core Particles.
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DOI：
10.1021/acs.biochem.6b01144
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发表时间：
2017-01-10
期刊：
影响因子：
2.9
通讯作者：
Greenberg MM
中科院分区：
文献类型：
--
作者：
Banerjee S;Chakraborty S;Jacinto MP;Paul MD;Balster MV;Greenberg MM
DNA在温和的碱性条件下在脱嘧啶/脱嘌呤位点被快速切割，但在磷酸盐缓冲液（pH 7.5）中半衰期为数周。然而，在核小体核心颗粒（NCP）中，脱碱基位点的反应性要高出约100倍。组蛋白催化链断裂，并且在超螺旋位置1.5处，组蛋白H4尾主要负责加速切割。当核小体核心颗粒是包含近端链断裂的双链损伤的一部分时，无碱基位点的链断裂速率常数在核小体核心颗粒中进一步增强。这种形式的切割导致高度有害的双链断裂。这种加速依赖于NCP中的无碱基病变的位置及其结构。在脱嘌呤/脱嘧啶位点处的切割速率的增强随着链断裂和脱碱基位点之间的距离增加而迅速下降，并且一旦两种形式的损伤分开7 bp，则可以忽略不计。然而，当差距的大小从一个核苷酸增加到两个核苷酸时，双链断裂形成速率的增强增加。相反，在双链病变内的2-脱氧核糖内酯的裂解率增强更温和，它是类似的游离DNA和核小体核心颗粒。我们推测，在核小体核心颗粒内含有脱嘌呤/脱嘧啶位点的双链病变处双链断裂形成的增强速率是一种普遍现象，并且是由于DNA灵活性增加。
DNA is rapidly cleaved under mild alkaline conditions at apyrimidinic/apurinic sites, but the half-life is several weeks in phosphate buffer (pH 7.5). However, abasic sites are ~100-fold more reactive within nucleosome core particles (NCPs). Histone proteins catalyze the strand scission, and at superhelical location 1.5, the histone H4 tail is largely responsible for the accelerated cleavage. The rate constant for strand scission at an abasic site is enhanced further in a nucleosome core particle when it is part of a bistranded lesion containing a proximal strand break. Cleavage of this form results in a highly deleterious double-strand break. This acceleration is dependent upon the position of the abasic lesion in the NCP and its structure. The enhancement in cleavage rate at an apurinic/apyrimidinic site rapidly drops off as the distance between the strand break and abasic site increases and is negligible once the two forms of damage are separated by 7 bp. However, the enhancement of the rate of double-strand break formation increases when the size of the gap is increased from one to two nucleotides. In contrast, the cleavage rate enhancement at 2-deoxyribonolactone within bistranded lesions is more modest, and it is similar in free DNA and nucleosome core particles. We postulate that the enhanced rate of double-strand break formation at bistranded lesions containing apurinic/apyrimidinic sites within nucleosome core particles is a general phenomenon and is due to increased DNA flexibility.