McCutcheon J P, Agrawal R K, Philips S M, Grassucci R A, Gerchman S E, Clemons W M, Ramakrishnan V, Frank J
Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, UT, 84132, USA.
Proc Natl Acad Sci U S A. 1999 Apr 13;96(8):4301-6. doi: 10.1073/pnas.96.8.4301.
The location of translational initiation factor IF3 bound to the 30S subunit of the Thermus thermophilus ribosome has been determined by cryoelectron microscopy. Both the 30S.IF3 complex and control 30S subunit structures were determined to 27-A resolution. The difference map calculated from the two reconstructions reveals three prominent lobes of positive density. The previously solved crystal structure of IF3 fits very well into two of these lobes, whereas the third lobe probably arises from conformational changes induced in the 30S subunit as a result of IF3 binding. Our placement of IF3 on the 30S subunit allows an understanding in structural terms of the biochemical functions of this initiation factor, namely its ability to dissociate 70S ribosomes into 30S and 50S subunits and the preferential selection of initiator tRNA by IF3 during initiation.
通过冷冻电子显微镜已确定与嗜热栖热菌核糖体30S亚基结合的翻译起始因子IF3的位置。30S.IF3复合物和对照30S亚基结构均确定为27埃分辨率。从这两种重建计算出的差异图显示出三个突出的正密度叶。IF3先前解析的晶体结构与其中两个叶非常吻合,而第三个叶可能是由于IF3结合导致30S亚基发生构象变化而产生的。我们将IF3定位在30S亚基上,有助于从结构角度理解该起始因子的生化功能,即其将70S核糖体解离为30S和50S亚基的能力以及IF3在起始过程中对起始tRNA的优先选择。