" Fusions with Histone H3 Result in Highly Specific Alteration of Gene Expression."
Nhuan Ha1, Karen Hellauer1, Bernard Turcotte1, 2, 3,
1Department of Medicine, Royal Victoria Hospital and 2Department of Biochemistry and 3Department of Microbiology and Immunology, McGill University, 687 Pine Avenue West, Montréal, Québec H3A 1A1, Canada
Abstract:
Hap1 is a yeast transcriptional activator which controls expression of genes such as CYC1 and CYC7. Our results show that Hap1 activity is dependent on a functional chromatin remodeling complex SWI/SNF. Using a modified two-hybrid screen with Hap1 as bait, we recovered expression vectors encoding the Gal4 activation domain fused to histone H3 [Gal4(AD)-H3]. Hap1 activity at CYC1 or CYC7 was increased by Gal4(AD)-H3 and the effect was dependent on the presence of the activation domain of Hap1 and a functional SWI complex. Importantly, overexpression of H3 alone had no effect on Hap1 activity. Analysis of Gal4(AD)-H3 revealed that the fusion is not incorporated into the nucleosome while a functional Gal4 activation domain is dispensable. Activity of many other transcriptional activators was unchanged or slightly affected in the presence of Gal4(AD)-H3. Thus, our results identify a new class of histone H3 variants that cause highly specific alteration of gene expression. Hap1 may interact directly with H3 favoring chromatin remodeling by the SWI/SNF complex.
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2. Benjamin W, Levander AD, Gellhorn A, and DeBellis RH, "An RNA-Histone Complex in Mammalian Cells and the Isolation of a New RNA Species", Proc. Natl. Acad. Sci. U.S.A. 55: 858 (1966).
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