RESUMEN
Chromatin remodelling complexes (CRC) are ATP-dependent molecular machines important for the dynamic organization of nucleosomes along eukaryotic DNA. CRCs SWI/SNF, RSC and INO80 can move positioned nucleosomes in promoter DNA, leading to nucleosome-depleted regions which facilitate access of general transcription factors. This function is strongly supported by transcriptional activators being able to interact with subunits of various CRCs. In this work we show that SWI/SNF subunits Swi1, Swi2, Snf5 and Snf6 can bind to activation domains of Ino2 required for expression of phospholipid biosynthetic genes in yeast. We identify an activator binding domain (ABD) of ATPase Swi2 and show that this ABD is functionally dispensable, presumably because ABDs of other SWI/SNF subunits can compensate for the loss. In contrast, mutational characterization of the ABD of the Swi2-related ATPase Sth1 revealed that some conserved basic and hydrophobic amino acids within this domain are essential for the function of Sth1. While ABDs of Swi2 and Sth1 define separate functional protein domains, mapping of an ABD within ATPase Ino80 showed co-localization with its HSA domain also required for binding actin-related proteins. Comparative interaction studies finally demonstrated that several unrelated activators each exhibit a specific binding pattern with ABDs of Swi2, Sth1 and Ino80.
Asunto(s)
Adenosina Trifosfatasas , Ensamble y Desensamble de Cromatina , Proteínas de Unión al ADN , Unión Proteica , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae , Factores de Transcripción , Activación Transcripcional , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Adenosina Trifosfatasas/genética , Adenosina Trifosfatasas/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Ensamble y Desensamble de Cromatina/genética , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Proteínas Cromosómicas no Histona/genética , Proteínas Cromosómicas no Histona/metabolismo , Regulación Fúngica de la Expresión Génica , Dominios Proteicos , Proteínas Nucleares , Proteínas de Ciclo Celular , Factores de Transcripción con Motivo Hélice-Asa-Hélice BásicoRESUMEN
Binding of general transcription factors TFIID and TFIIA to basal promoters is rate-limiting for transcriptional initiation of eukaryotic protein-coding genes. Consequently, activator proteins interacting with subunits of TFIID and/or TFIIA can drastically increase the rate of initiation events. Yeast transcriptional activator Ino2 interacts with several Taf subunits of TFIID, among them the multifunctional Taf1 protein. In contrast to mammalian Taf1, yeast Taf1 lacks bromodomains which are instead encoded by separate proteins Bdf1 and Bdf2. In this work, we show that Bdf1 not only binds to acetylated histone H4 but can also be recruited by Ino2 and unrelated activators such as Gal4, Rap1, Leu3 and Flo8. An activator-binding domain was mapped in the N-terminus of Bdf1. Subunits Toa1 and Toa2 of yeast TFIIA directly contact sequences of basal promoters and TFIID subunit TBP but may also mediate the influence of activators. Indeed, Ino2 efficiently binds to two separate structural domains of Toa1, specifically with its N-terminal four-helix bundle structure required for dimerization with Toa2 and its C-terminal ß-barrel domain contacting TBP and sequences of the TATA element. These findings complete the functional analysis of yeast general transcription factors Bdf1 and Toa1 and identify them as targets of activator proteins.