13 Yeast RNA Polymerase II Transcription In Vitro: General Initiation Factors; Novel Mediator of Transcriptional Activation; Three-dimensional Structure of RNA Polymerase II

Abstract

OVERVIEW
In yeast as in higher organisms, a set of protein factors is required in addition to RNA polymerase II (pol II) for accurate initiation of transcription at a promoter. A further protein factor, referred to as a mediator, is required for the enhancement of transcription by all activator proteins tested. Structural studies of the yeast RNA pol II transcription apparatus have so far revealed the surface topography of the polymerase molecule at about 12–16 Å resolution. Grooves and channels that may accommodate double- and single-stranded DNA and RNA are apparent.

INTRODUCTION
Five years ago we reported the preparation of a yeast extract that supported accurate initiation of transcription at RNA pol II promoters (Lue and Kornberg 1987). This initial observation has led to (1) the resolution and reconstitution of a set of general initiation factors that cooperate with pol II in the transcription of a minimal promoter (Flanagan et al. 1990); (2) the discovery of a novel mediator, required in addition to the general initiation factors and pol II for transcription responsive to activator proteins (Kornberg et al. 1989; Kelleher et al. 1990); and (3) the crystallization and three-dimensional structure determination of a functional form of pol II (Edwards et al. 1990; Darst et al. 1991). We describe here the course of these developments and their implications for the mechanism of pol II transcription, for regulation of the process, and for related DNA transactions.

Studies of initiation by pol II in vitro began more than 10 years ago...