Identification and characterization of CIA/ASF1 as an interactor of bromodomains associated with TFIID

Abstract

General transcription initiation factor IID (TFIID) plays a central and critical role in transcription initiation from both naked and chromatin templates. Although interaction between several DNAbinding proteins and TFIID were identified and well characterized, functional linkage between TFIID and chromatin factors has remained to be elucidated. Here we show the identification and characterization of human CIA͞hASF1 (identified previously as a histone chaperone) as an interactor of two tandem bromodomain modules of human (h)TAF II250͞CCG1, the largest subunit of TFIID. Although yeast (y)TAF II145, a homologue of hTAFII250͞CCG1 in Saccharomyces cerevisiae, lacks bromodomains, glutathione Stransferase pull-down and immunoprecipitation assays revealed that Asf1p (antisilencing function 1), the counterpart of CIA in S. cerevisiae, interacts with Bdf1p (bromodomain factor 1), which is reported to serve as the missing bromodomain in yTAFII145. Furthermore, yeast strain lacking the BDF1 gene shows the Spt phenotype that is shown also by the ASF1 gene disruptant, and a double-knockout strain of both genes shows synthetic lethality, indicating that ASF1 genetically interacts with bromodomains associated with yTFIID. We also found that Asf1p coprecipitates with yTFIID subunits from yeast whole-cell extract, and overexpression of yTFIID subunits suppress the Spt phenotype caused by gene disruption of the ASF1. This study describes the functional linkage between TFIID and a histone chaperone. Chromosomal DNA in eukaryotes is packaged into chromatin, and the nucleosome is the fundamental structural unit of chromatin (1). Nucleosomes act as general repressors of transcription by RNA polymerase II, which transcribes proteincoding genes in eukaryotic cells (2-4). Initiation of transcription by RNA polymerase II is a multistep reaction in which several general transcription initiation factors are involved (5). Transcription initiation factor IID (TFIID) is the only general transcription initiation factor that specifically binds the TATA box that is found within the promoter of many mRNA-encoding genes and required for specific transcription initiation both in vivo and in vitro. Therefore it is suggested that binding of TFIID to the promoter is a crucial step for eukaryotic transcriptional regulation (6-8). To date, numerous functional interactions between TFIID and DNA binding activators͞repressors have been characterized (7-10). Functional interactions between TFIID and chromatin factors have remained to be elucidated, although they have been anticipated from studies showing that TFIID is not capable of binding to preassembled nucleosomes in vitro (11). Recently it was reported that histone acetyltransferase (HAT)-containing complexes and nucleosome remodeling factors affect the binding of TFIID to nucleosomal DNA templates (12,13).Biochemical studies have demonstrated that TFIID is a multisubunit complex comprised of TBP, the TATA box-binding protein, and several TBP-associated factors (TAF II s; refs. 14-16). TAF II 250͞cell ...

Binding of the histone chaperone ASF1 to the CBP bromodomain promotes histone acetylation

“…The histone chaperone ASF1 has been shown previously to bind to bromodomains (29), but the mode of interaction with the CBP bromodomain is quite distinct from that observed with the CCG1 bromodomain (30). We find that the interaction between the CBP bromodomain and ASF1 and the interaction between ASF1 and histones promoted histone acetylation on free histones.…”

“…5A). ASF1A previously has been shown to bind to the bromodomain of the CCG1 protein (29). Therefore, we wondered whether the bromodomain of CBP is important for the interaction with ASF1.…”

The Histone Chaperone Anti-silencing Function 1 Stimulates the Acetylation of Newly Synthesized Histone H3 in S-phase

“…However, no direct interaction between Asf1 and Gcn5 has been reported so far. Asf1 has been reported to bind to the bromodomain-containing proteins Brd1 and Brd2 in yeast and Brahma in Drosophila (24,25). As Gcn5 does contain a bromodomain (26), it may be a potential binding partner of Asf1 that merits further investigation in the future.…”

Histone chaperone ASF1 cooperates with the Brahma chromatin-remodelling machinery

“…First, mutation of the yeast asf1 gene results in the suppression of S-phase-specific histone genes activation (Sutton et al 2001). Second, it was shown that ASF1 interacts with bromodomain-containing subunits of TFIID (Munakata et al 2000;Chimura et al 2002).…”