MBF1 serves as a transcriptional coactivator of Trachea defective/Apontic during development of the trachea and central nervous system in Drosophila melanogaster. Q. Liu , M. Jindra , H. Ueda , Y. Hiromi , S. Hirose. Department of Developmental Genetics, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka-ken 411-8540, Japan. 81-559-81-6773.

   Multiprotein bridging factor 1 (MBF1) is a transcriptional coactivator that interconnects certain sequence-specific regulators and TATA-binding protein (TBP). The MBF1 sequence is highly conserved across species from yeast Saccharomyces cerevisiae to human. In yeast, MBF1 mediates GCN4-dependent transactivation. However, biological functions of Drosophila MBF1 are not well understood. In this study, we made a transgenic fly line which is capable of expressing FLAG-tagged MBF1 and isolated MBF1-associated proteins from embryonic nuclear extracts using an anti-FLAG antibody. One of them was identified to be a bZIP protein Trachea defective (TDF)/Apontic (APT). We show that TDF/APT is a sequence-specific transcriptional activator and that MBF1 mediates the activation through direct interaction with TDF/APT and TBP. Furthermore, genetic interaction between tdf and mbf1 implicates TDF/APT and MBF1 in proper development of the trachea and central nervous system (CNS).