RIBOSOME STRUCTURE DETERMINED BY ELECTRON-MICROSCOPY OF ESCHERICHIA-COLI SMALL SUBUNITS, LARGE SUBUNITS AND MONOMERIC RIBOSOMES
RIBOSOME STRUCTURE DETERMINED BY ELECTRON-MICROSCOPY OF ESCHERICHIA-COLI SMALL SUBUNITS, LARGE SUBUNITS AND MONOMERIC RIBOSOMES
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DOI：
10.1016/0022-2836(76)90200-x
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发表时间：
1976-01-01
影响因子：
5.6
通讯作者：
LAKE, JA
中科院分区：
文献类型：
--
作者：
LAKE, JA
通过对核糖体及亚基以及抗体标记的核糖体及亚基进行电子显微镜观察，确定了大肠杆菌小亚基、大亚基和单体核糖体独特的三维结构。小亚基在C底物上定向，其长轴平行于C平面。在这些投影中，该亚基被一个类似于在真核小亚基中观察到的聚集的负染区域分为1/3和2/3两部分。四种特征性视图或投影很容易被识别，它们对应于围绕亚基长轴大约 -40°、0°、+50°和 +110°的取向。两种最具特色的视图是一种准对称视图（0°），其特征是一条近似的镜像对称线与亚基长轴重合；以及一种不对称视图（110°），其特征是有一个凹的和一个凸的亚基边界。在不对称投影中，可以正面看到一个平台或壁架。该平台附着在亚基下部2/3处，刚好在1/3 - 2/3分界线下方。它在分界线处与亚基上部1/3分开，在分界线之上它形成一个大约30 - 40埃宽的裂缝，此前该裂缝被认为是密码子 - 反密码子相互作用的位点。大亚基呈现出四种特征性视图。最显著的准对称视图（θ = 90°，φ = 0°）的特征是位于一条近似镜像对称线上的中央突起。中央突起被在其两侧大约呈50°倾斜的突出特征所环绕。这些突起中较小的一个呈杆状，大约40埃宽，100埃长。从中央突起另一侧突出的特征比杆状附属物更短、更钝且更宽。在另一个与准对称投影大致正交的视图，即不对称投影（θ = 10°，φ = 90°）中，亚基轮廓的特征是下边缘凸起，上边界有一个缺口。在投影中，亚基被缺口分为两个不等的区域。较小的区域约占总投影密度的20%，由中央突起和杆状附属物组成。在单体70S核糖体区域中观察到的轮廓是30S和50S轮廓叠加的结果。观察到两种主要视图，一种是重叠视图，一种是非重叠视图，这取决于70S轮廓中小亚基的轮廓是否与大亚基的轮廓重叠。在单体核糖体中，小亚基的定向使得平台与大亚基接触。在70S核糖体的重叠视图中，大亚基的中央突起与小亚基上部1/3的一部分重叠，尽管在三维空间中它们可能被30 - 50埃分开。小亚基的一个包含平台、裂缝和上部1/3部分的区域，被认为是IF3和IF2的大致结合位点，位于大小亚基之间的界面处，在小亚基的一个靠近但可能与大亚基没有物理接触的区域。
Unique, 3-dimensional structures were determined for E. coli small subunits, large subunits and monomeric ribosomes by EM of ribosomes and subunits and of antibody-labeled ribosomes and subunits. Small subunits orient on the C substrate with their long axes parallel to the plane of the C. In these projections the subunit is divided into a 1/3 and a 2/3 portion by a region of accumulated negative stain similar to that observed in eukaryotic small subunits. Four characteristic views, or projections, are readily recognized and correspond to orientations of approximately -40.degree., 0.degree., +50.degree. and +110.degree. about the long axis of the subunit. The 2 most distinctive views are a quasi-symmetric view (0.degree.) that is characterized by an approximate line of mirror symmetry that coincides with the long axis of the subunit and an asymmetric view (110.degree.) that is characterized by a concave and a convex subunit boundary. In the asymmetric projection, a platform or ledge is viewed face-on. The platform is attached to the lower 2/3 of the subunit just below the 1/3-2/3 partition. It is separated from the upper 1/3 of the subunit at the level of the partition and above the partition it forms a cleft .apprx. 30-40 .ANG. wide, which was previously suggested as the site of the codon-anticodon interaction. Four characteristic views are presented for the large subunit. The most prominent quasi-symmetric view (.theta. = 90.degree., .vphi. = 0.degree.) is distinguished by a central protuberance located on a line of approximate mirror symmetry. The central protuberance is surrounded by projecting features inclined at .apprx. 50.degree. on both sides of it. The smaller of these projections is rod-like, .apprx. 40 .ANG. wide and .apprx. 100 .ANG. long. The feature projecting from the other side of the central protuberance is shorter, more blunt and wider than the rod-like appendage. In another view approximately orthogonal to the quasi-symmetric projection, the asymmetric projection (.theta. = 10.degree., .vphi. = 90.degree.), the subunit profile is distinguished by a convex lower edge and an upper boundary which is indented by a notch. The subunit is separated, in projection, by the notch into 2 unequal regions. The smaller region comprises .apprx. 20% of the total projected density and consists of the central protuberance and the rod-like appendage. The profiles observed in fields of monomeric 70 S ribosomes result from superpositions of the 30 S and 50 S profiles. Two major views are observed, an overlap and a non-overlap view, corresponding to whether or not the profile of the small subunit overlaps that of the large subunit in the 70 S profile. The small subunit is oriented in the monomeric ribosome so that the platform is in contact with the large subunit. The central protuberance of the large subunit overlaps part of the upper 1/3 of the small subunit in the overlap view of 70 S ribosomes, although in 3 dimensions they are probably separated by 30-50 .ANG.. A region of the small subunit comprising the platform, the cleft and part of the upper 1/3, suggested to be the approximate binding site of IF3 and IF2, is located at the interface between the large and small subunits, in a region of the small subunit that is close to, but probably not in physical contact with, the large subunit.