DNA-DEPENDENT PROTEIN-KINASE - A POTENT INHIBITOR OF TRANSCRIPTION BY RNA-POLYMERASE-I
DNA-DEPENDENT PROTEIN-KINASE - A POTENT INHIBITOR OF TRANSCRIPTION BY RNA-POLYMERASE-I
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DOI：
10.1101/gad.9.2.193
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发表时间：
1995-01-15
影响因子：
10.5
通讯作者：
GRUMMT, I
中科院分区：
文献类型：
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作者：
KUHN, A;GOTTLIEB, TM;GRUMMT, I
DNA依赖性蛋白激酶（DNA-PK）由一个分子量约为350 kD的催化亚基（p350）和一个称为Ku的DNA结合组分组成。虽然DNA-PK可以磷酸化许多转录因子，但迄今为止还没有报道这种酶在转录中的功能。在这里，我们表明，DNA-PK强烈抑制RNA聚合酶I（Pol I）的转录。DNA-PK的转录抑制需要ATP水解，并且DNA-PK必须与Pol I转录机制共定位在相同的DNA分子上。与DNA-PK需要DNA末端的活性一致，转录抑制仅有效地发生在线性化模板上。包括单轮转录、失败起始测定和在加尾模板上的因子非依赖性转录的机制研究证明DNA-PK抑制起始（即，第一个磷酸二酯键的形成），但不影响转录延伸。转录的抑制涉及转录起始复合物的磷酸化，并且拯救实验揭示失活的因子保持与启动子结合，从而防止起始复合物的形成。我们讨论了这些研究结果在体内rRNA合成的控制方面可能的相关性。
DNA-dependent protein kinase (DNA-PK) comprises a catalytic subunit of similar to 350 kD (p350) and a DNA-binding component termed Ku. Although DNA-PK can phosphorylate many transcription factors, no function for this enzyme in transcription has been reported thus far. Here, we show that DNA-PK strongly represses transcription by RNA polymerase I (Pol I). Transcriptional repression by DNA-PK requires ATP hydrolysis, and DNA-PK must be colocalized on the same DNA molecule as the Pol I transcription machinery. Consistent with DNA-PK requiring DNA ends for activity, transcriptional inhibition only occurs effectively on linearized templates. Mechanistic studies including single-round transcriptions, abortive initiation assays, and factor-independent transcription on a tailed template demonstrate that DNA-PK inhibits initiation (i.e., the formation of the first phosphodiester bonds) but does not affect transcription elongation. Repression of transcription involves phosphorylation of the transcription initiation complex, and rescue experiments reveal that the inactivated factor remains bound to the promoter and thus prevents initiation complex formation. We discuss the possible relevance of these findings in regard to the control of rRNA synthesis in vivo.