PDF(Pubmed)
Abstract：
The essential Mediator (MED) coactivator complex plays a well-understood role in regulation of basal transcription in all eukaryotes, but the mechanism underlying its role in activator-dependent transcription remains unknown. We investigated modulation of metazoan MED interaction with RNA polymerase II (RNA Pol II) by antagonistic effects of the MED26 subunit and the CDK8 kinase module (CKM). Biochemical analysis of CKM-MED showed that the CKM blocks binding of the RNA Pol II carboxy-terminal domain (CTD), preventing RNA Pol II interaction. This restriction is eliminated by nuclear receptor (NR) binding to CKM-MED, which enables CTD binding in a MED26-dependent manner. Cryoelectron microscopy (cryo-EM) and crosslinking-mass spectrometry (XL-MS) revealed that the structural basis for modulation of CTD interaction with MED relates to a large intrinsically disordered region (IDR) in CKM subunit MED13 that blocks MED26 and CTD interaction with MED but is repositioned upon NR binding. Hence, NRs can control transcription initiation by priming CKM-MED for MED26-dependent RNA Pol II interaction.
摘要：
必需介体（MED）共激活复合物在所有真核生物的基础转录调控中起着众所周知的作用，但其在激活因子依赖性转录中的作用机制尚不清楚.我们研究了MED26亚基和CDK8激酶模块（CKM）的拮抗作用对后生动物MED与RNA聚合酶II（RNAPolII）相互作用的调节。CKM-MED的生化分析表明，CKM阻断了RNAPolII羧基末端结构域（CTD）的结合，防止RNAPolII相互作用。通过与CKM-MED结合的核受体（NR）消除了这种限制，这使得CTD能够以MED26依赖性方式结合。冷冻电子显微镜（cryo-EM）和交联质谱（XL-MS）显示，调节CTD与MED相互作用的结构基础与CKM亚基MED13中的一个大的内在无序区域（IDR）有关，该区域阻断了MED26和CTD与MED的相互作用，但在NR结合后重新定位。因此，NRs可以通过引发CKM-MED以进行MED26依赖性RNAPolII相互作用来控制转录起始。
