The role of Swi/Snf at the HO promoter: new insights.
Doyel Mitra, David Stillman
Department of Pathology, University of Utah, 30 North 1900 East, Salt Lake City, UT, 84132, U.S.A.
The HO gene has a large, complex promoter that undergoes complicated regulation. Activators of HO expression include the Swi5 and SBF DNA-binding proteins, the Mediator complex, and the Swi/Snf and Gcn5 (SAGA) chromatin factors. It has been shown that these factors bind to the HO promoter in a specific sequence, with binding being dependent on other factors (1-3). We have now also used alpha factor to synchronize the cell cycle, and examined factor binding at the HO promoter in the second cycle after release. We find important differences in how specific mutations affect factor binding, which will be discussed in detail, and thus the current model for factor binding to the HO promoter requires revision. Many of the earlier experiments were performed using cells synchronized by withdrawal, followed by return, of Cdc20, using a GAL:CDC20 allele. It is possible that overexpression of Cdc20 from the GAL:CDC20 allele, before the arrest, affects the M phase in these cells and later affects HO . We observe Swi/Snf binding to the HO TATA element, and this binding is reduced in a gcn5 mutant, providing a new role for Gcn5 in HO activation. 1. Cosma et al 1999 Cell 97:299 2. Cosma et al 2001 Mol Cell 7:1213 3. Bhoite et al 2001 G&D 15:2457.
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