title: Crystal structure, biochemical and genetic characterization of yeast and E. cuniculi TAF(II)5 N-terminal domain: implications for TFIID assembly.
abstract: General transcription factor TFIID plays an essential role in transcription initiation by RNA polymerase II at numerous promoters. However, understanding of the assembly and a full structural characterization of this large 15 subunit complex is lacking. TFIID subunit TAF(II)5 has been shown to be present twice in this complex and to be critical for the function and assembly of TFIID. Especially, the TAF(II)5 N-terminal domain is required for its incorporation within TFIID and immuno-labelling experiments carried out by electron microscopy at low resolution have suggested that this domain might homodimerize, possibly explaining the three-lobed architecture of TFIID. However, the resolution at which the electron microscopy (EM) analyses were conducted is not sufficient to determine whether homodimerization occurs or whether a more intricate assembly implying other subunits is required. Here we report the X-ray structures of the fully evolutionary conserved C-terminal sub-domain of the TAF(II)5 N terminus, from yeast and the mammalian parasite Encephalitozoon cuniculi. This sub-domain displays a novel fold with specific surfaces having conserved physico-chemical properties that can form protein-protein interactions. Although a crystallographic dimer implying one of these surfaces is present in one of the crystal forms, several biochemical analyses show that this sub-domain is monomeric in solution, even at various salt conditions and in presence of different divalent cations. Consequently, the N-terminal sub-domain of the TAF(II)5 N terminus, which is homologous to a dimerization motif but has not been fully conserved during evolution, was studied by analytical ultracentrifugation and yeast genetics. Our results show that this sub-domain dimerizes at very high concentration but is neither required for yeast viability, nor for incorporation of two TAF(II)5 molecules within TFIID and for the assembly of this complex. Altogether, although our results do not argue in favour of a homodimerization of the TAF(II)5 N-terminal domain, our structural analyses suggest a role for this domain in assembly of TFIID and its related complexes SAGA, STAGA, TFTC and PCAF.
authors.affiliation: Institut de Génétique et Biologie Moléculaire et Cellulaire (IGBMC), Département de Biologie et Génomique Structurales, 1 rue Laurent Fries, B.P. 10142, 67404 Illkirch Cedex, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Romier
authors.forename: Nicole
authors.initials: N
authors.lastname: James
authors.forename: Catherine
authors.initials: C
authors.lastname: Birck
authors.forename: Jean
authors.initials: J
authors.lastname: Cavarelli
authors.forename: Christian
authors.initials: C
authors.lastname: Vivarès
authors.forename: Martine A
authors.initials: MA
authors.lastname: Collart
authors.forename: Dino
authors.initials: D
authors.lastname: Moras
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018797:Cell Cycle Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D009670:Encephalitozoon cuniculi / Q000737:chemistry*; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D035381:TATA-Binding Protein Associated Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D035181:TATA-Box Binding Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D035362:Transcription Factor TFIID / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D005656:Fungal Proteins; D021122:Protein Subunits; C115017:SPT15 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C438897:TAF5 protein, S cerevisiae; D035381:TATA-Binding Protein Associated Factors; D035181:TATA-Box Binding Protein; D035362:Transcription Factor TFIID