MBF2 was first isolated from the silkworm Bombyx mori as a positive cofactor that activates transcription through its interaction with TFIIA. To identify conserved domain(s) within the MBF2 molecule, we isolated cDNAs encoding MBF2 homologues from other silkworms Bombyx mandarina and Samia cynthia. Bacterially expressed and purified MBF2 of B. mandarina and S. cynthia activated transcription in vitro. The predicted amino acid sequences of MBF2 from two Bombyx species share 97% homology. When we compared between B. mori and S. cynthia factors, the homology reduced to 50%. Four regions in MBF2 are conserved among these three species. Two of them are present in the middle region of MBF2 that is essential for the transcriptional activation.
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