1 Genome Structure and Organization in Saccharomyces cerevisiae

Abstract

I. INTRODUCTION
A relatively simple picture is emerging of the structure of the yeast genome. With the important exception of mating-type interconversion, the genome seems to be quite stable: Other DNA rearrangements appear to be infrequent and of peripheral significance to the yeast life cycle. Genes are tightly packed, with little “spacer” DNA and strikingly few pseudogenes. There is no extensive clustering of functionally related or coordinately regulated genes. Genetic distance is largely proportional to physical distance, at least when averaged over tens or hundreds of kilobase pairs. Finally, the cis-acting sequences required for chromosome function—telomeres, centromeres, and replication origins—are only a few hundred base pairs long and function in almost any context.

This overview has emerged after 15 years of recombinant DNA work on yeast. Recombinant DNA techniques have favored a divide and conquer approach to the yeast genome; hence, the present perspective may overemphasize the trees at the expense of the forest. Nevertheless, the view of the yeast chromosomes as a series of nearly independent functional units (like “beads on a string”) has been a productive working model. Several recent reviews have covered aspects of the structural and functional organization of the yeast genome. Two articles by Newlon (1988 Newlon (1989) provide particularly broad coverage.

II. THE YEAST GENOME: VITAL STATISTICS
The basic features of the yeast genome are summarized in Table 1. The best estimate of the genome size comes from physical mapping of the chromosomes with restriction endonucleases that cleave yeast DNA infrequently (Link and...