Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Science. 2010 Jan 8;327(5962):206-9. doi: 10.1126/science.1182015. Epub 2009 Nov 12.
Previous x-ray crystal structures have given insight into the mechanism of transcription and the role of general transcription factors in the initiation of the process. A structure of an RNA polymerase II-general transcription factor TFIIB complex at 4.5 angstrom resolution revealed the amino-terminal region of TFIIB, including a loop termed the "B finger," reaching into the active center of the polymerase where it may interact with both DNA and RNA, but this structure showed little of the carboxyl-terminal region. A new crystal structure of the same complex at 3.8 angstrom resolution obtained under different solution conditions is complementary with the previous one, revealing the carboxyl-terminal region of TFIIB, located above the polymerase active center cleft, but showing none of the B finger. In the new structure, the linker between the amino- and carboxyl-terminal regions can also be seen, snaking down from above the cleft toward the active center. The two structures, taken together with others previously obtained, dispel long-standing mysteries of the transcription initiation process.
先前的 X 射线晶体结构揭示了转录的机制以及一般转录因子在起始过程中的作用。一个分辨率为 4.5 埃的 RNA 聚合酶 II-通用转录因子 TFIIB 复合物的结构揭示了 TFIIB 的氨基末端区域，包括一个称为“B 手指”的环，延伸到聚合酶的活性中心，它可能与 DNA 和 RNA 相互作用，但该结构显示了羧基末端区域的很少部分。在不同溶液条件下获得的同一复合物的新晶体结构分辨率为 3.8 埃，与前一个结构互补，揭示了 TFIIB 的羧基末端区域，位于聚合酶活性中心裂缝上方，但没有显示 B 手指。在新结构中，还可以看到氨基末端和羧基末端区域之间的连接体，从裂缝上方蜿蜒向下伸向活性中心。这两个结构与之前获得的其他结构一起，消除了转录起始过程中由来已久的谜团。
