Functional interaction of the c-Myc transactivation domain with the TATA binding protein: evidence for an induced fit model of transactivation domain folding.
c-Myc is a member of a family of sequence specific-DNA binding proteins that are thought to regulate the transcription of genes involved in normal cell growth, differentiation, and apoptosis. In order to understand how human c-myc functions as a transcription factor, we have studied the mechanism of action and structure of the N-terminal transactivation domain, amino acids 1-143. In a protein interaction assay, c-myc1-143 bound selectively to two basal transcription factors, the TATA binding protein (TBP) and the RAP74 subunit of TFIIF. Furthermore, the isolated c-myc transactivation domain competed for limiting factors required for the assembly of a functional preinitiation complex. This squelching of basal transcription was reversed in a dose-dependent manner by recombinant TBP. Taken together, these results identify TBP as an important target for the c-myc transactivation domain, during transcriptional initiation. Similar to other transactivation domains, the c-myc1-143 polypeptide showed little or no evidence of secondary structure, when measured by circular dichroism spectroscopy (CD) in aqueous solution. However, significant alpha-helical conformation was observed in the presence of the hydrophobic solvent trifluoroethanol. Strikingly, addition of TBP caused changes in the CD spectra consistent with induction of protein conformation in c-myc1-143 during interaction with the target factor. This change was specific for TBP as a similar effect was not observed in the presence of TFIIB. These data support a model in which target factors induce or stabilize a structural conformation in activator proteins during transcriptional transactivation.
McEwan
I J
IJ
Department of Biosciences, Karolinska Institute, NOVUM, Huddinge, Sweden. iain.mcewan@cbt.ki.se
Dahlman-Wright
K
K
Ford
J
J
Wright
A P
AP
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D002942:Circular Dichroism; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D016271:Proto-Oncogene Proteins c-myc / Q000737:chemistry* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D012697:Serine Endopeptidases / Q000378:metabolism; D016385:TATA Box; D035181:TATA-Box Binding Protein; D014157:Transcription Factors / Q000378:metabolism*; D019473:Transcription Factors, TFII; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D000099160:LexA Repressor Protein
D001426:Bacterial Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D010446:Peptide Fragments; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D012697:Serine Endopeptidases; D035181:TATA-Box Binding Protein; D014157:Transcription Factors; D019473:Transcription Factors, TFII; D000099160:LexA Repressor Protein; C056604:transcription factor TFIIF