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Structure of the complete elongation complex of RNA polymerase II with basal factors

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Science  01 Sep 2017:
Vol. 357, Issue 6354, pp. 921-924
DOI: 10.1126/science.aan8552

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Transcription machinery remains steadfast

Eukaryotic transcription of mRNA is a multistep process mediated by RNA polymerase II (Pol II). Pol II combines with several other factors to form an elongation complex that promotes transcription elongation. Ehara et al. determined the high-resolution structure of the elongation complex by means of x-ray crystallography and cryo-electron microscopy (see the Perspective by Fouqueau and Werner). Multiple elongation factors are distributed on a wide surface of Pol II and establish an RNA exit path and DNA entry or exit tunnels, which facilitate nascent transcript transfer and DNA unwinding or rewinding. The Pol II elongation complex thus adopts a stable architecture suitable for processive transcription.

Science, this issue p. 921; see also p. 871

Abstract

In the early stage of transcription, eukaryotic RNA polymerase II (Pol II) exchanges initiation factors with elongation factors to form an elongation complex for processive transcription. Here we report the structure of the Pol II elongation complex bound with the basal elongation factors Spt4/5, Elf1, and TFIIS. Spt4/5 (the Spt4/Spt5 complex) and Elf1 modify a wide area of the Pol II surface. Elf1 bridges the Pol II central cleft, completing a “DNA entry tunnel” for downstream DNA. Spt4 and the Spt5 NGN and KOW1 domains encircle the upstream DNA, constituting a “DNA exit tunnel.” The Spt5 KOW4 and KOW5 domains augment the “RNA exit tunnel,” directing the exiting nascent RNA. Thus, the elongation complex establishes a completely different transcription and regulation platform from that of the initiation complexes.

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