"Transcription factor IID (TFIID) is a key player in regulated transcription of eukaryotic genes by RNA polymerase II. The scaffold of TFIID is composed of a number of TATA-box binding protein-associated factors (TAFs), which are also found in other multimeric transcription factors (e.g. SAGA). An elaborate system of decision-making therefore must occur that directs the assembly of TAFs into either TFIID or SAGA or other TAF containing complexes. Recently, a multimeric 400 kDa small TAF-containing complex, SMAT, was discovered. SMAT is proposed to be a potent regulator of committed TFIID and SAGA assembly. The objective of this proposal is to elucidate the role of SMAT in eukaryotic gene regulation by means of an integrated, interdisciplinary approach combining structural, biochemical and in vivo cell biology methods. SMAT and its subcomplexes will be produced recombinantly by state-of-the-art eukaryotic expression techniques. Stable variants of SMAT core-complexes will be identified by a novel limited proteolysis/mass spectrometric approach and translated into expression experiments by utilizing an automated cloning platform technology. Intensive screening for growth of single, well diffracting crystals will be performed at the high-throughput crystallization facility at EMBL. By combining synchrotron X-ray crystallography, electron microscopy and small angle X-ray scattering experiments, a molecular model of SMAT will be obtained. Based on this model, point mutations will be designed, which specifically destabilize SMAT. Effects of the mutant proteins and of posttranslational modifications on the cellular decision-making process of TFIID or SAGA assembly, as well as SMAT integrity, will be assessed by in vivo functional assays in HeLa cells. The interdisciplinary nature of this project promises to contribute to the applicant’s career development by diversifying his competences and refining his skills ultimately guiding him towards an independent leading position."