New insights into the function of transcription factor TFIID from recent structural studies

Abstract

The general transcription factor IID is a key player in the early events of gene expression. TFIID is a multisubunit complex composed of the TATA binding protein and at least 13 TBP associated factors (TAfs) which recognize the promoter of protein coding genes in an activator dependant way. This review highlights recent findings on the molecular architecture and dynamics of TFIID. The structural analysis of functional transcription complexes formed by TFIID, TFIIA, activators and/or promoter DNA illuminates the faculty of TFIID to adjust to various promoter architectures and highlights its role as a platform for preinitiation complex assembly.

Figure 1

Subunit composition of yeast TFIID The known atomic structures of Taf domains or their homology models are shown along with a bulky representation of the non crystallized parts of the Tafs as circles whose sizes are proportional to the length of the remaining aminoacid chains. Circles representing histone-fold containing Tafs are colored pink. The different subunits were roughly positioned according to the available protein-protein interaction data and immunolabelling results. The atomic structures shown represent a characteristic HFD heterodimers for Taf4-12, Taf6-9 Taf10-8, Taf11-13 and Taf10-3; the structure of TBP complexed with the TAND domain of Taf1, the Leukotriene A4 hydrolase domain homologuous to Taf2; a characteristic WD40 propeller domain found in Taf5 and the NTD2 domain of Taf5.

Figure 2

Cryo electron microscopy models of TFIID. Comparison of the TFIID models derived from from Schizosaccharomyces pombe [32], Saccharomyces cerevisiae [30] and human [31]. The lobes were labeled according to the S. cerevisiae structure and may be different for the other models. The deposited S. pombe density map appeared significantly smaller and was rescaled according to the published size. The bar represents 10 nm.

Figure 3

Mapping functional sites on TFIID. The positions of Taf subunits involved in DNA contacts are represented in red and the transcriptional activator binding sites are depicted in blue on the yeast TFIID. The positions of the human activator binding sites were inferred from the alignment of the yeast and human TFIID models.