Abstract
Multiprotein bridging factor 1 (MBF1) is known to be a transcriptional co-activator that mediates transcriptional activation by bridging between an activator and a TATA-box binding protein (TBP). Although amino acid sequences of MBF1 are evolutionarily conserved among eucaryotes, the function of MBF1 in plant is poorly understood. Arabidopsis thaliana, which has three subtypes of MBF1 genes, is the first example among all organisms. We demonstrated that expression of every three AtMBF1 partially rescues the yeast mbf1 mutant phenotype and every AtMBF1 directly binds to TBP and GCN4, indicating that all of them function as co-activators for GCN4-dependent transcriptional activation. We also report that each of their subtypes shows distinct tissue-specific expression patterns and responses to phytohormones. These observations suggest that even though they share a similar biochemical function, each MBF1 has distinct roles in various tissues and conditions. We will discuss roles of MBF1 in Arabidopsis.
