2 Yeast RNA Polymerase Subunits and Genes

Abstract

OVERVIEW
Yeast RNA polymerases A(I), B(II), and C(III) are organized around a common core of subunits related to the bacterial core enzyme (β′ βα₂) and share a set of five small subunits (ABC27, ABC23, ABC14.5, ABC10α, and ABC10β). All these subunits are essential for growth. In addition, each enzyme contains a variable number of enzyme-specific subunits, some of which are not strictly required for growth. Most subunit genes have been cloned, sequenced, and mutagenized to produce null alleles and, for several of them, conditional mutants. A functional map of RNA polymerase active site, taken in a broad sense, has begun to emerge from a combined genetic and biochemical analysis of the large subunits.

GENERAL PROPERTIES OF YEAST NUCLEAR RNA POLYMERASES
The budding yeast Saccharomyces cerevisiae, with its biochemically and genetically well-characterized transcription apparatus, is currently the most suitable experimental model for a comprehensive study of eukaryotic RNA polymerases (see Sentenac 1985; Gabrielsen and Sentenac 1991 and references therein; Young 1991; Thuriaux and Sentenac 1992). Yeast RNA polymerases are typically eukaryotic in their subunit complexity, and there is a fair degree of functional equivalence between the transcription machinery of yeasts and of metazoan eukaryotes (see, e.g., Struhl 1989; Sawadogo and Sentenac 1990; and other chapters in this volume). We assume, therefore, that what is learned of the yeast enzymes may largely be extrapolated to other eukaryotes. Several chapters of this volume cover important structural and functional features of the RNA polymerases of higher eukaryotes and of associated general transcription factors (Corden...