2 Chromosomal DNA Replication

Abstract

I. INTRODUCTION
A consistent theme in the first edition of this series (Strathern et al. 1981Strathern et al. 1982) was the potential of yeast as a model eukaryote. During the past few years, much of the promise of yeast as a model for eukaryotic DNA replication has been realized. The long-standing question of whether there are specific origins of replication in chromosomal DNA has been answered by the demonstration that replication initiates at or close to several autonomously replicating sequence (ARS) elements in ribosomal DNA (rDNA) and on chromosome III. From the analysis of large segments of chromosomes, a picture of the spatial and temporal activation of replicons is beginning to emerge. The analysis of ARS elements has progressed to the point that nucleotide sequences required for origin function can be at least partially specified. Progress has also been made in identifying and characterizing proteins that function in DNA replication, particularly DNA polymerases and topoisomerases. In virtually every respect examined, yeast replication proteins are homologous to replication proteins from other eukaryotes, further validating yeast as a model system.

The features of yeast that make it particularly attractive for the study of DNA replication include its small genome size and the unparalleled power of its genetic system. The small size of yeast chromosomes, which are nevertheless typical of the larger chromosomes of other eukaryotes in organization and replication pattern, has facilitated cloning and mapping large segments of chromosomes. Cloning of chromosomal elements such as centromeres and telomeres was made easier by their relatively...