3 The Protein Biosynthesis, Elongation Cycle

Abstract

The detailed mechanism of protein biosynthesis has been studied for many years, especially in prokaryotic systems, but in recent years also increasingly in eukaryotes. The reader is referred to recent books on various aspects of protein biosynthesis in general (Hill et al. 1990; Nierhaus et al. 1993a; Söll and RajBhandary 1995). Protein biosynthesis as it happens on the ribosome is conveniently divided into three phases: initiation, elongation, and termination. Here we are primarily concerned with the description of the elongation cycle from a functional and structural point of view (for discussion of the regulation of the elongation cycle, see Chapter 24. Aspects of initiation and termination are only dealt with to illustrate some important concepts of elongation, which seem to be general for all three phases. Aminoacylation of tRNA catalyzed by tRNA-synthetases is not described nor discussed in this review. Readers are referred to recent reviews on this subject (Arnez and Moras 1997; Cusack 1997). Because the amount of work performed over many years is enormous, many important biochemical studies on the function of elongation factors are not mentioned in detail, but a discussion of some of these can be found in a recent book chapter (Clark et al. 1995).

During the last six years, major advances have been made in generating a structural description of the prokaryotic elongation cycle. Currently available is an essentially complete structural picture of most of the major functional forms of the elongation factors (Krab and Parmeggiani 1998). Many of the structural principles found in...