Functional Organization of the 30S Ribosomal Subunit

Abstract

INTRODUCTION
Studies of ribosome structure have as their principal goal an understanding of the mechanism of protein synthesis. An ancillary, but by no means uninteresting, aspect of the ribosome is its assembly. Indeed, that aspect of ribosome structure which so thoroughly complicates the analysis of ribosome function is precisely the property which makes its assembly so fascinating, namely, its complexity. One objective of the present chapter is to suggest that what we have learned about the mechanism of ribosome assembly provides important clues to the functional organization of the ribosome.

Although most attempts to attribute specific functional contributions to individual ribosomal components have centered around the proteins, I will suggest that it is the RNA which may provide the more interesting active sites of the ribosome. Of course, enzymatic functions such as peptidyl transferase and the nucleoside triphosphate esterase activities that are expressed in the course of protein synthesis must be protein activities. However, the characteristic functions of the ribosome are not these enzymatic ones. It is the binding of specific aminoacyl-tRNA molecules, complexed with factors, and the movement of these macromolecules to different sites, all guided by coded signals in the messenger RNA, that constitute the unique functions of ribosomes. Here the contributions of ribosomal RNA may have been obscured by a number of accidents.

Once each of the ribosomal proteins has been purified and thoroughly characterized, it is easy enough to reconstitute ribosomes with each of the proteins missing in turn or to study the effects of chemical...