5vkl

Structural highlights

Function

[SPT6_YEAST] Plays a role in maintenance of chromatin structure during RNA polymerase II transcription elongation thereby repressing transcription initiation from cryptic promoters. Mediates the reassembly of nucleosomes onto the promoters of at least a selected set of genes during repression; the nucleosome reassembly is essential for transcriptional repression. Essential for viability.^{[1] [2] [3] [4]} [RPB1_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.

References

1. ↑ Hartzog GA, Wada T, Handa H, Winston F. Evidence that Spt4, Spt5, and Spt6 control transcription elongation by RNA polymerase II in Saccharomyces cerevisiae. Genes Dev. 1998 Feb 1;12(3):357-69. PMID:9450930
2. ↑ Kaplan CD, Laprade L, Winston F. Transcription elongation factors repress transcription initiation from cryptic sites. Science. 2003 Aug 22;301(5636):1096-9. PMID:12934008 doi:http://dx.doi.org/10.1126/science.1087374
3. ↑ Kaplan CD, Holland MJ, Winston F. Interaction between transcription elongation factors and mRNA 3'-end formation at the Saccharomyces cerevisiae GAL10-GAL7 locus. J Biol Chem. 2005 Jan 14;280(2):913-22. Epub 2004 Nov 5. PMID:15531585 doi:http://dx.doi.org/10.1074/jbc.M411108200
4. ↑ Adkins MW, Tyler JK. Transcriptional activators are dispensable for transcription in the absence of Spt6-mediated chromatin reassembly of promoter regions. Mol Cell. 2006 Feb 3;21(3):405-16. PMID:16455495 doi:http://dx.doi.org/S1097-2765(05)01852-6
5. ↑ Sdano MA, Fulcher JM, Palani S, Chandrasekharan MB, Parnell TJ, Whitby FG, Formosa T, Hill CP. A novel SH2 recognition mechanism recruits Spt6 to the doubly phosphorylated RNA polymerase II linker at sites of transcription. Elife. 2017 Aug 16;6. pii: e28723. doi: 10.7554/eLife.28723. PMID:28826505 doi:http://dx.doi.org/10.7554/eLife.28723