The assembly of promoter-specific preinitiation complexes, which requires protein-DNA and protein-protein interactions, is an important step in regulation of gene expression in eukaryotes. Multiprotein bridging factor 1 (MBF1) is a transcriptional coactivator, which mediates the interaction of the TATA binding protein (TBP) in the preinitiation complex and gene-specific activators. In order to understand the functions of MBF-1 in the filamentous fungus Trichoderma reseei (TrMBF1), we are studying its solution structure, and the interaction with TrTBP, by high resolution NMR. TrMBF1 was cloned and over expressed in E. coli. The whole protein was shown to be very unstable, however the stability was increased by removing the N-terminal segment. This is in agreement with the fact that an unstable N-terminal segment with a well folded C-terminal domain was observed in other organisms such as in the human and yeast. The N-terminal domain shows less conservation within different organisms, and it does not participate in binding to TBP. By using PolyHis-Tagged Pull-Down assay we showed that TrTBP interacts specifically with the whole TrMBF1. But the other co-activator that binds to TrMBF1 forming a ternary complex with TrTBP is unknown. A good dispersion of HN cross peaks was observed in the ¹⁵N HSQC spectrum of the C-terminal domain of TrMBF1 (CTD-TrMBF1; AA 56-151), indicating that it is well folded in solution. This is in confirmed by the observation of several short range HN-HN NOE cross peaks in 2D NOE and 3D ¹⁵N NOESY-HSQC spectra. Sequential assignment of backbone resonances of CTD-TrMBF1 is being carried out using triple-resonance multidimensional NMR experiments on a ¹³C,¹⁵N labeled sample.  Titration experiments of CTD-TrMBF1 and TrTBP will be performed and followed by NMR, in order to confirm the biochemical data, and map the complex interface.