RNA Polymerases and Transcriptive Specificity in Saccharomyces cerevisiae

Abstract

INTRODUCTION
The genomes of animal cells typically contain several hundred times the DNA of prokaryotic cells. Because of this high genetic complexity, the detection of specific gene products in transcripts from chromatin or purified DNA templates is very difficult. In addition, most eukaryotic cells contain low concentrations of the molecular components involved in the transcriptional process. To partially obviate these problems we have chosen the simple eukaryote Saccharomyces cerevisiae to study eukaryotic transcriptional control. The yeast genome is comparatively small, only three to four times that of Escherichia coli (Ogur et al. 1952). Thus it is possible to quantitate the concentration of a unique RNA sequence even in a totally random transcript from yeast DNA. Our approach was to reconstruct transcriptive specificity from purified molecules. Since yeast cells can be easily obtained in large amounts, this facilitates the isolation of components involved in the transcriptional process.

The presence of multiple forms of RNA polymerase in eukaryotic cells, together with their unique function and cellular location, indicates that these enzymes may play a critical role in selective transcription. The enzyme multiplicity could, however, be related to other functions, such as localization on the chromosome, rather than to a direct involvement in initiation or termination at specific promoters. The role of the RNA polymerases can best be ascertained by testing the ability of the purified enzymes to transcribe a defined template. Most of the studies to date have focused on the transcription of ribosomal genes, which are reiterated in the genome of...