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Productive and Nonproductive Complexes of Ku and DNA-Dependent Protein Kinase at DNA Termini

机译：生产和非生产的Ku和DNA依赖蛋白激酶的蛋白依赖复合物。

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DNA-dependent protein kinase (DNA-PK) is the only eukaryotic protein kinase known to be specifically activated by double-stranded DNA (dsDNA) termini, accounting for its importance in repair of dsDNA breaks and its role in physiologic processes involving dsDNA breaks, such as V(D)J recombination. In this study we conducted kinase and binding analyses using DNA-PK on DNA termini of various lengths in the presence and absence of Ku. We confirmed our previous observations that DNA-PK can bind DNA termini in the absence of Ku, and we determined rate constants for binding. However, in the presence of Ku, DNA-PK can assume either a productive or a nonproductive configuration, depending on the length of the DNA terminus. For dsDNA greater than 26 bp, the productive mode is achieved and Ku increases the affinity of the DNA-PK for the Ku:DNA complex. The change in affinity is achieved by increases in both the kinetic association rate and reduction in the kinetic dissociation rate. For dsDNA smaller than 26 bp, the nonproductive mode, in which DNA-PK is bound to Ku:DNA but is inactive as a kinase, is assumed. Both the productive and nonproductive configurations are likely to be of physiologic importance, depending on the distance of the dsDNA break site to other protein complexes, such as nucleosomes.
机译：DNA依赖性蛋白激酶（DNA-PK）是已知唯一被双链DNA（dsDNA）末端特异性激活的真核蛋白激酶，这说明其在修复dsDNA断裂中的重要性及其在涉及dsDNA断裂的生理过程中的作用，例如V（D）J重组。在这项研究中，我们在存在和不存在Ku的情况下，使用DNA-PK对各种长度的DNA末端进行了激酶和结合分析。我们证实了我们先前的观察结果，即在不存在Ku的情况下，DNA-PK可以结合DNA末端，并确定了结合的速率常数。但是，在Ku的存在下，取决于DNA末端的长度，DNA-PK可以呈现生产性或非生产性构型。对于大于26 bp的dsDNA，可实现生产模式，Ku可提高DNA-PK对Ku：DNA复合物的亲和力。亲和力的变化通过动力学缔合速率的增加和动力学解离速率的降低来实现。对于小于26 bp的dsDNA，假定为非生产模式，其中DNA-PK与Ku：DNA结合，但作为激酶无效。根据dsDNA断裂位点与其他蛋白质复合物（如核小体）之间的距离，生产性和非生产性构型均可能具有重要的生理意义。

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