Interaction between TATA-binding protein (TBP) and multiprotein bridging factor-1 (MBF1) from the filamentous insect pathogenic fungus Beauveria bassiana

Abstract

TATA-binding protein (TBP) is a ubiquitous component of eukaryotic transcription factorsthat acts to nucleate assembly and position pre-initiation complexes. Multiprotein bridging factor 1 (MBF1) is thought to interconnect TBP with gene specific transcriptional activators, modulating transcriptional networks in response to specific signal and developmental programs. The insect pathogen, Beauveria bassiana, is a cosmopolitan fungus found in mostecosystems where it acts as an important regulator of insect populations and can form intimate associations with certain plants. In order to gain a better understanding of the functionof MBF1 in filamentous fungi, its interaction with TBP was demonstrated. The MBF1 and TBP homologs in B. bassiana were cloned and purified from a heterologous E. coli expressionsystem. Whereas purified BbTBP was shown to be able to bind oligonucleotide sequences containing the TATA-motif (Kd ≈ 1.3 nM) including sequences derived from thepromoters of the B. bassiana chitinase and protease genes. In contrast, BbMBF1 was unable to bind to these same target sequences. However, the formation of a ternary complexbetween BbMBF1, BbTBP, and a TATA-containing target DNA sequence was seen in agarose gel electrophoretic mobility shift assays (EMSA). These data indicate that BbMBF1forms direct interactions with BbTBP, and that the complex is capable of binding to DNA sequences containing TATA-motifs, confirming that BbTBP can link BbMBF1 to targetsequences as part of the RNA transcriptional machinery in fungi. Copyright: