Taatjes Dylan J, Näär Anders M, Andel Frank, Nogales Eva, Tjian Robert
Howard Hughes Medical Institute and, Lawrence Berkeley National Laboratory, Department of Molecular and Cell Biology, 401 Barker Hall, University of California, Berkeley, CA 94720, USA.
Science. 2002 Feb 8;295(5557):1058-62. doi: 10.1126/science.1065249.
The human cofactor complexes ARC (activator-recruited cofactor) and CRSP (cofactor required for Sp1 activation) mediate activator-dependent transcription in vitro. Although these complexes share several common subunits, their structural and functional relationships remain unknown. Here, we report that affinity-purified ARC consists of two distinct multisubunit complexes: a larger complex, denoted ARC-L, and a smaller coactivator, CRSP. Reconstituted in vitro transcription with biochemically separated ARC-L and CRSP reveals differential cofactor functions. The ARC-L complex is transcriptionally inactive, whereas the CRSP complex is highly active. Structural determination by electron microscopy (EM) and three-dimensional reconstruction indicate substantial differences in size and shape between ARC-L and CRSP. Moreover, EM analysis of independently derived CRSP complexes reveals distinct conformations induced by different activators. These results suggest that CRSP may potentiate transcription via specific activator-induced conformational changes.
人类辅因子复合物ARC（激活因子招募的辅因子）和CRSP（Sp1激活所需的辅因子）在体外介导依赖激活因子的转录。尽管这些复合物共享几个共同的亚基，但其结构和功能关系仍不清楚。在这里，我们报告亲和纯化的ARC由两个不同的多亚基复合物组成：一个较大的复合物，称为ARC-L，和一个较小的共激活因子CRSP。用生化分离的ARC-L和CRSP进行体外转录重建，揭示了不同的辅因子功能。ARC-L复合物无转录活性，而CRSP复合物高度活跃。通过电子显微镜（EM）和三维重建进行的结构测定表明，ARC-L和CRSP在大小和形状上存在显著差异。此外，对独立获得的CRSP复合物的EM分析揭示了不同激活因子诱导的不同构象。这些结果表明，CRSP可能通过特定的激活因子诱导的构象变化增强转录。
