Ribosome Structure Investigated by Digital Accumulation and Processing of Ribosome Tetramer Images

Abstract

Electron microscopic observation of ribosomes, especially combined with 3-D reconstruction methods, may reveal structural relationships among components of the ribosome. In such studies it is necessary to average over a large number of specimen particles, to enhance the predominant structure while suppressing local irregularities of specimen preservation and staining, and to reduce the statistical insufficiencies of individual low-dose electron micrographs. One very successful method makes use of an average over the particles in a two-dimensional crystalline layer, but if the particles are not well organized, the resolution is reduced. Organization of crystalline arrays can be enhanced by computer methods, but if computational alignment is used it seems most profitable to avoid the restriction to crystalline spec- iment completely and work with isolated particles. A fixed orientation is still helpful; so in studying ribosomes, which lack their own symmetry, we have chosen to observe ribosome tetramers. The tetramers, units of the chick embryo ribosome crystal, present a fixed view in the electron micrograph.