Structural insights into transcription initiation by RNA polymerase II

• Models for the architecture of the RNA Pol II preinitiation complex and open complex are discussed.
• General factors TFIIB and TFIIF function in part through allosteric regulation of Pol II.
• A DNA translocase activity is proposed to open DNA strands during initiation.
• Eukaryotic Pols share a conserved core initiation complex.
• New progress in understanding the interface between coactivators and the core transcription machinery is described.

Transcriptional regulation is one of the most important steps in control of cell identity, growth, differentiation, and development. Many signaling pathways controlling these processes ultimately target the core transcription machinery that, for protein coding genes, consists of RNA polymerase II (Pol II) and the general transcription factors (GTFs). New studies on the structure and mechanism of the core assembly and how it interfaces with promoter DNA and coactivator complexes have given tremendous insight into early steps in the initiation process, genome-wide binding, and mechanisms conserved for all nuclear and archaeal Pols. Here, we review recent developments in dissecting the architecture of the Pol II core machinery with a focus on early and regulated steps in transcription initiation.