Fu J, Gnatt A L, Bushnell D A, Jensen G J, Thompson N E, Burgess R R, David P R, Kornberg R D
Department of Structural Biology, Stanford University School of Medicine, Fairchild Science Center, California 94305, USA.
Cell. 1999 Sep 17;98(6):799-810. doi: 10.1016/s0092-8674(00)81514-7.
Appropriate treatment of X-ray diffraction from an unoriented 18-heavy atom cluster derivative of a yeast RNA polymerase II crystal gave significant phase information to 5 A resolution. The validity of the phases was shown by close similarity of a 6 A electron density map to a 16 A molecular envelope of the polymerase from electron crystallography. Comparison of the 6 A X-ray map with results of electron crystallography of a paused transcription elongation complex suggests functional roles for two mobile protein domains: the tip of a flexible arm forms a downstream DNA clamp; and a hinged domain may serve as an RNA clamp, enclosing the transcript from about 8-18 residues upstream of the 3'-end in a tunnel.
对酵母RNA聚合酶II晶体的无定向18重原子簇衍生物进行适当的X射线衍射处理，可得到分辨率达5埃的重要相位信息。通过6埃电子密度图与电子晶体学得到的聚合酶16埃分子包络的高度相似性，证明了这些相位的有效性。将6埃X射线图与暂停转录延伸复合物的电子晶体学结果进行比较，表明两个可移动蛋白质结构域具有功能作用：柔性臂的末端形成下游DNA钳；一个铰链结构域可能作为RNA钳，在一个通道中围绕3'-末端上游约8 - 18个残基处的转录本。
