Eukaryotic transcription initiation

Abstract

Why such complexity in Pol II transcription? The 60 protein requirement for Pol II transcription does not reflect the complexity of RNA synthesis. After all, the chemistry of the transcription reaction in prokaryotic and eukaryotic organisms is, in essence, identical. Yet bacterial transcription is catalyzed by a five subunit core complex — α2ββ′ω, comparable to eukaryotic Rpb1,2,3,6,11 — with promoter recognition conferred by one of only a handful of different σ subunits that associate with the core enzyme. Instead, the complexity of the eukaryotic Pol II machinery is a consequence of both the organization of the eukaryotic genome, including the packaging of DNA into chromatin, and the myriad regulatory parameters that control gene expression.The challenge that lies ahead is to unravel the physical interactions that occur among and within the different transcription complexes and how these interactions occur in response to different stimuli. High-resolution three-dimensional images have provided remarkable insight into the structural basis of Pol II function. However, the size, complexity and dynamic nature of the TFIID, TFIIH and MED complexes make it unlikely that high-resolution images of these intact complexes will be forthcoming. Instead, new technologies, including novel methods for crosslinking protein–protein and protein–DNA interactions, are likely to illuminate the structural basis of transcription in small, but highly informative increments.