Ribosome Structure as Studied by Electron Microscopy

Abstract

INTRODUCTION Much has been learned of the events occurring during ribosome function, but it is still difficult to correlate the sequence of macromolecular interactions involved in protein synthesis with the chemical composition of ribosomes. Presently individual functions are being assigned to ribosomal components, but our understanding of the operation of the translational machinery will only be complete when this information can be related to structural features. It is likely that this goal will be obtained through the use of ribosome crystals suitable for electron microscopy and X-ray diffraction, as well as by direct visualization of protein sites on ribosomes using specific antibodies. We have studied biochemically and electron microscopically the ribosome crystal which can be induced by cooling chicken embryos in ovo (Byers 1966Byers 1967) and investigated the conditions leading to ribosome crystallization in vivo and in vitro. Our observations (Morimoto, Blobel and Sabatini 1972a,b) and those of other authors (Byers 1971; Carey 1970; Carey and Read 1971) indicate that crystals from chicken embryos are a promising subject for investigating the structure of ribosomes since they are made of normal 80S particles, which, although inactive, are potentially functional. Here we present a summary of our electron microscopic studies on crystals of chicken embryo ribosomes. In addition, in light of the large amount of interest in E. coli ribosomes and in consideration of the relatively advanced state of our biochemical knowledge of them, we present the preliminary results of our comparative electron microscopic structural studies on eukaryotic (Nonomura, Blobel and Sabatini...