Yoon Sungpil, Qiu Hongfang, Swanson Mark J, Hinnebusch Alan G
Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, NIH, Bethesda, Maryland 20892, USA.
Mol Cell Biol. 2003 Dec;23(23):8829-45. doi: 10.1128/MCB.23.23.8829-9945.2003.
The nucleosome remodeling complex SWI/SNF is a coactivator for yeast transcriptional activator Gcn4p. We provide strong evidence that Gcn4p recruits the entire SWI/SNF complex to its target genes ARG1 and SNZ1 but that SWI/SNF is dispensable for Gcn4p binding to these promoters. It was shown previously that Snf2p/Swi2p, Snf5p, and Swi1p interact directly with Gcn4p in vitro. However, we found that Snf2p is not required for recruitment of SWI/SNF by Gcn4p nor can Snf2p be recruited independently of other SWI/SNF subunits in vivo. Snf5p was not recruited as an isolated subunit but was required with Snf6p and Swi3p for optimal recruitment of other SWI/SNF subunits. The results suggest that Snf2p, Snf5p, and Swi1p are recruited only as subunits of intact SWI/SNF, a model consistent with the idea that Gcn4p makes multiple contacts with SWI/SNF in vivo. Interestingly, Swp73p is necessary for efficient SWI/SNF recruitment at SNZ1 but not at ARG1, indicating distinct subunit requirements for SWI/SNF recruitment at different genes. Optimal recruitment of SWI/SNF by Gcn4p also requires specific subunits of SRB mediator (Gal11p, Med2p, and Rox3p) and SAGA (Ada1p and Ada5p) but is independent of the histone acetyltransferase in SAGA, Gcn5p. We suggest that SWI/SNF recruitment is enhanced by cooperative interactions with subunits of SRB mediator and SAGA recruited by Gcn4p to the same promoter but is insensitive to histone H3 acetylation by Gcn5p.
核小体重塑复合物SWI/SNF是酵母转录激活因子Gcn4p的共激活因子。我们提供了有力证据表明，Gcn4p将整个SWI/SNF复合物招募至其靶基因ARG1和SNZ1，但SWI/SNF对于Gcn4p与这些启动子的结合并非必需。先前研究表明，Snf2p/Swi2p、Snf5p和Swi1p在体外可直接与Gcn4p相互作用。然而，我们发现Snf2p并非Gcn4p招募SWI/SNF所必需，且在体内Snf2p不能独立于其他SWI/SNF亚基而被招募。Snf5p并非作为单个亚基被招募，而是与Snf6p和Swi3p一起，对于其他SWI/SNF亚基的最佳招募是必需的。这些结果表明，Snf2p、Snf5p和Swi1p仅作为完整SWI/SNF的亚基被招募，这一模型与Gcn4p在体内与SWI/SNF进行多次接触的观点一致。有趣的是，Swp73p对于在SNZ1高效招募SWI/SNF是必需的，但在ARG1则不然，这表明在不同基因处招募SWI/SNF对亚基有不同的要求。Gcn4p对SWI/SNF的最佳招募还需要SRB中介体（Gal11p、Med2p和Rox3p）和SAGA（Ada1p和Ada5p）的特定亚基，但独立于SAGA中的组蛋白乙酰转移酶Gcn5p。我们认为，通过与Gcn4p招募至同一启动子的SRB中介体和SAGA亚基的协同相互作用，SWI/SNF的招募得以增强，但对Gcn5p介导的组蛋白H3乙酰化不敏感。
