Transcriptional activation through interaction of MBF2 with TFIIA.
BACKGROUND
Transcriptional activation of the Drosopohila melanogaster fushi tarzu gene by FTZ-F1 or its silkworm counterpart BmFTZ-F1 requires two cofactors MBF1 and MBF2 which do not directly bind to DNA. MBF1 is a bridging molecule that connects FTZ-F1 (or BmFTZ- F1), MBF2 and TATA binding protein TBP. MBF2 is a positive cofactor that activates transcription.


RESULTS
To elucidate the mechanism of transcriptional activation by MBF2, we isolated a cDNA coding for the factor. Northern blot analyses showed temporally restricted expression of MBF2 mRNA similar to that of BmFTZ-F1 mRNA. The cDNA sequence predicts a polypeptide of 10 kDa whereas natural MBF2 is a glycoprotein of 22 kDa. The deduced amino acid sequence of the factor showed no homology with proteins in the databases. Farwestern analyses and glutathione S-transferase interaction assays demonstrated that MBF2 makes a direct contact with the beta-subunit of TFIIA. In a HeLa cell nuclear extract, bacterially expressed recombinant MBF2 activated transcription from various promoters as natural MBF2 did. This activation requires the MBF2-TFIIA interaction. When recombinant MBF2 was added to the HeLa cell nuclear extract in the presence of MBF1 and FTZ622 bearing the DNA-binding region of FTZ-F1, it selectively activated transcription of the fushi tarazu gene. This selective activation also requires the MBF2-TFIIA interaction.


CONCLUSIONS
MBF2 activates transcription through its interaction with TFIIA. Selective transcriptional activation occurs when MBF2 is recruited to a promoter carrying the FTZ-F1 binding site by FTZ-F1 and MBF1.
Li
F Q
FQ
Department of Developmental Genetics, National Institute of Genetics, Mishima, Shizuoka-ken, Japan.
Takemaru
K
K
Goto
M
M
Ueda
H
H
Handa
H
H
Hirose
S
S
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D012831:Bombyx; D003001:Cloning, Molecular; D018076:DNA, Complementary; D029721:Drosophila Proteins; D051717:Fushi Tarazu Transcription Factors; D005786:Gene Expression Regulation; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000235:genetics; D006801:Humans; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D013329:Structure-Activity Relationship; D035561:Transcription Factor TFIIA; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D018076:DNA, Complementary; D029721:Drosophila Proteins; D051717:Fushi Tarazu Transcription Factors; D006023:Glycoproteins; D018398:Homeodomain Proteins; D019476:Insect Proteins; C491471:MBF2 protein, Drosophila; C106979:MBF2 protein, insect; D035561:Transcription Factor TFIIA; D014157:Transcription Factors