4bxx
From Proteopedia
Arrested RNA polymerase II-Bye1 complex
Structural highlights
FunctionRPB1_YEAST DNA-dependent RNA polymerase catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates. Largest and catalytic component of RNA polymerase II which synthesizes mRNA precursors and many functional non-coding RNAs. Forms the polymerase active center together with the second largest subunit. Pol II is the central component of the basal RNA polymerase II transcription machinery. During a transcription cycle, Pol II, general transcription factors and the Mediator complex assemble as the preinitiation complex (PIC) at the promoter. 11-15 base pairs of DNA surrounding the transcription start site are melted and the single stranded DNA template strand of the promoter is positioned deeply within the central active site cleft of Pol II to form the open complex. After synthesis of about 30 bases of RNA, Pol II releases its contacts with the core promoter and the rest of the transcription machinery (promoter clearance) and enters the stage of transcription elongation in which it moves on the template as the transcript elongates. Pol II appears to oscillate between inactive and active conformations at each step of nucleotide addition. Elongation is influenced by the phosphorylation status of the C-terminal domain (CTD) of Pol II largest subunit (RPB1), which serves as a platform for assembly of factors that regulate transcription initiation, elongation, termination and mRNA processing. Pol II is composed of mobile elements that move relative to each other. The core element with the central large cleft comprises RPB3, RBP10, RPB11, RPB12 and regions of RPB1 and RPB2 forming the active center. The clamp element (portions of RPB1, RPB2 and RPB3) is connected to the core through a set of flexible switches and moves to open and close the cleft. A bridging helix emanates from RPB1 and crosses the cleft near the catalytic site and is thought to promote translocation of Pol II by acting as a ratchet that moves the RNA-DNA hybrid through the active site by switching from straight to bent conformations at each step of nucleotide addition. In elongating Pol II, the lid loop (RPB1) appears to act as a wedge to drive apart the DNA and RNA strands at the upstream end of the transcription bubble and guide the RNA strand toward the RNA exit groove located near the base of the largely unstructured CTD domain of RPB1. The rudder loop (RPB1) interacts with single stranded DNA after separation from the RNA strand, likely preventing reassociation with the exiting RNA. The cleft is surrounded by jaws: an upper jaw formed by portions of RBP1, RPB2 and RPB9, and a lower jaw, formed by RPB5 and portions of RBP1. The jaws are thought to grab the incoming DNA template, mainly by RPB5 direct contacts to DNA. Publication Abstract from PubMedBypass of Ess1 (Bye1) is a nuclear protein with a domain resembling the central domain in the transcription elongation factor TFIIS. Here we show that Bye1 binds with its TFIIS-like domain (TLD) to RNA polymerase (Pol) II, and report crystal structures of the Bye1 TLD bound to Pol II and three different Pol II-nucleic acid complexes. Like TFIIS, Bye1 binds with its TLD to the Pol II jaw and funnel. In contrast to TFIIS, however, it neither alters the conformation nor the in vitro functions of Pol II. In vivo, Bye1 is recruited to chromatin via its TLD and occupies the 5'-region of active genes. A plant homeo domain (PHD) in Bye1 binds histone H3 tails with trimethylated lysine 4, and this interaction is enhanced by the presence of neighboring posttranslational modifications (PTMs) that mark active transcription and conversely is impaired by repressive PTMs. We identify putative human homologs of Bye1, the proteins PHD finger protein 3 and death-inducer obliterator, which are both implicated in cancer. These results establish Bye1 as the founding member of a unique family of chromatin transcription factors that link histones with active PTMs to transcribing Pol II. Structures of RNA polymerase II complexes with Bye1, a chromatin-binding PHF3/DIDO homologue.,Kinkelin K, Wozniak GG, Rothbart SB, Lidschreiber M, Strahl BD, Cramer P Proc Natl Acad Sci U S A. 2013 Sep 3. PMID:24003114[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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