9 Initiation of Transcription by RNA Polymerase II

Abstract

OVERVIEW
Initiation of transcription by RNA polymerase II (pol II) requires the formation of a complex containing the basal factors TFIID, TFIIB, TFIIE/F, and polymerase. Additional factors have been suggested as important for initiation, and the relationship among these factors has not been well defined. The initiation complex is assembled in an ordered pathway commencing with the binding of TFIID and TFIIA to the TATA element. Interactions between polymerase and TFIIF in solution stimulate the binding of polymerase to the template-associated complex containing TFIID and TFIIB. This interaction also generates a polymerase-DNA conformation similar to that previously characterized for “open” prokaryotic polymerase-promoter complexes. Such a complex can rapidly initiate transcription, and its formation is rate-limiting for many prokaryotic promoters. Transcription factors that bind specific sequences in the vicinity of a promoter stimulate or suppress the rate of initiation through modulation of the basal reaction. The rate-limiting step in this basal process probably varies between different promoters, and thus there may be multiple mechanisms by which transcription factors regulate initiation.

INTRODUCTION
Intricate and important processes such as development and oncogenesis cannot be understood without considering the process of transcription initiation in some detail. A sufficiently precise model may soon be at hand. Several of the general transcription factors have been cloned, and the molecular events leading to transcription initiation by RNA pol II are slowly emerging.

The model of initiation presented here is based on studies using a minimal pol II promoter, defined as a TATA element and an initiation site....