The Yeast Ribosome: Structure, Function, and Synthesis

Abstract

INTRODUCTION
The ribosome holds our fascination for a number of reasons. It is a complex organelle, yet one that is comprehensible in terms of the number and stoichiometry of its constituent molecules. Its synthesis involves major interactions of nucleus and cytoplasm. It is ubiquitous in living cells, and as the site of protein synthesis, it plays a central role in cell growth and maintenance. The regulation of its synthesis is complex, not only because of the number of components involved, but also because it is closely tied to cell growth. Perhaps more important, the ribosome has been highly conserved during evolution and is the prime example of a “housekeeping enzyme.” A comparison of the regulation of ribosome synthesis in prokaryotes, in simple eukaryotes, and in complex eukaryotes may provide insight into the way regulation itself has evolved.

This paper consists of three parts: (1) the mature ribosome; (2) what is known of the way it works in protein synthesis, which for yeast is precious little; and (3) ribosome synthesis, including a considerable body of data concerning its regulation in yeast and a hypothesis to account for some of the data. Mitochondrial ribosomes are discussed by Dujon (1981).

THE YEAST RIBOSOME
Ribosomal RNA
Saccharomyces is typical of eukaryotes in that it has four species of RNA in its ribosome: 25S, 5.8S, and 5S in the 60S subunit, and 18S in the 40S subunit. The properties of these molecules are summarized in Table 1. The sequence of 5S RNA from S. carlsbergensis...