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Ribosome Structure and tRNA Binding Sites

James A. Lake


During the last decade, knowledge of ribosome structure has evolved from a 100-Å resolution structure obtained by three-dimensional reconstruction (Lake and Slayter 1970Lake and Slayter 1972; Unwin 1977) to current models for the Escherichia coli 70S ribosome at 30- to 40-Å resolution (Lake 1976; Tischendorf et al. 1976) derived by immunoelectron microscopy (for a review, see Lake 1978). This progress has resulted, in large part, from the convergence of different approaches toward studying ribosome structure and function, including biochemical, genetic, immunological, neutron-diffraction, and electron microscopic techniques (for a review, see Nomura et al. 1974). This paper reviews the relationship between ribosome structure and function with special reference to tRNA binding and the molecular events of protein synthesis.

Small Subunits, Large Subunits, and Monomeric Ribosomes
The structures of the small and large subunits of the E. coli ribosome are illustrated in Figure 1. The small subunit (Fig. 1a,b) is divided into two unequal parts by an indentation and a region of accumulated negative stain (Lake et al. 1974b). The parts are referred to as the upper one-third and the lower two-thirds. A region of the subunit, called the platform, extends from the lower two-thirds of the small subunit and forms a cleft between it and the upper one-third (Lake and Kahan 1976). Recent tilting experiments have determined the absolute hand of the 30S subunit (the correct enantiomorph is shown in Fig. 1) and have confirmed its asymmetric properties (Leonard and Lake 1979).

The large subunit, like the small subunit, is...

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