Regulation of HO gene expression in the yeast Saccharomyces cerevisiae is intricately orchestrated by an assortment of gene-specific DNA-binding and non-DNA binding regulators. Binding of the early G1 transcription factor Swi5 to the distal URS1 element of the HO promoter initiates a cascade of events through recruitment of the Swi/Snf and SAGA complexes. In late G1, binding of transcription factor SBF to promoter proximal sequences results in the timely expression of HO. In this work we describe an important additional layer of complexity to the current model by identifying a connection between Swi5 and the Mediator/RNA polymerase II holoenzyme complex. We show that Swi5 recruits Mediator to HO by specific interaction with the Gal11 module of the Mediator complex. Importantly, binding of both the Gal11 and Srb4 mediator components to the upstream region of HO is independent of the SBF factor. Swi/Snf is required for Mediator binding, and genetic suppression experiments suggest that Swi/Snf and Mediator act in the same genetic pathway of HO activation. Experiments examining the kinetics of binding show that Mediator binds to HO promoter elements 1.5 kb upstream of the transcription start site in early G1, but this binding occurs without RNA Pol II. RNA Pol II does not bind to HO until late G1, when HO is actively transcribed, and binding occurs exclusively to the TATA region.
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| Gene/Complex | Qualifier | Gene Ontology Term | Annotation Extension | Evidence | Source | Assigned On |
|---|---|---|---|---|---|---|
| SWI5 | enables | mediator complex binding | has input GAL11 | IPI with GAL11 | SGD | 2013-08-07 |
| SWI5 | enables | mediator complex binding | IMP | SGD | 2013-08-07 | |
| SWI5 | enables | DNA-binding transcription factor activity, RNA polymerase II-specific | IMP | SGD | 2018-04-11 |
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| Evidence ID | Analyze ID | Interactor | Interactor Systematic Name | Interactor | Interactor Systematic Name | Allele | Assay | Annotation | Action | Phenotype | SGA score | P-value | Source | Reference | Note |
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Increase the total number of rows showing on this page by using the pull-down located below the table, or use the page scroll at the table's top right to browse through the table's pages; use the arrows to the right of a column header to sort by that column; filter the table using the "Filter" box at the top of the table; click on the small "i" buttons located within a cell for an annotation to view further details about experiment type and any other genes involved in the interaction.