The activation function-1 of hepatocyte nuclear factor-4 is an acidic activator that mediates interactions through bulky hydrophobic residues.
The hepatocyte nuclear factor-4 (HNF-4) contains two transcription activation domains. One domain, activation function-1 (AF-1), consists of the extreme N-terminal 24 amino acids and functions as a constitutive autonomous activator of transcription. This short transactivator belongs to the class of acidic activators, and it is predicted to adopt an amphipathic alpha-helical structure. Transcriptional analysis of sequential point mutations of the negatively charged residues (Asp and Glu) revealed a stepwise decrease in activity, while mutation of all acidic residues resulted in complete loss of transcriptional activity. Mutations of aromatic and hydrophobic amino acids surrounding the negatively charged residues had a much more profound effect than mutations of acidic amino acids, since even a single mutation of these residues resulted in a dramatic decrease in transactivation, thus demonstrating the importance of hydrophobic residues in AF-1 activity. Like other acidic activators, the AF-1 of HNF-4 binds the transcription factor IIB and the TATA-binding protein directly in vitro. In addition, the cAMP-response-element-binding-protein, a transcriptional adapter involved in the transactivation of a plethora of transcription factors, interacts with the AF-1 of HNF-4 and co-operates in the process of transactivation by HNF-4. The different protein targets of AF-1 suggest that the AF-1 of HNF-4 may be involved in recruiting both general transcription factors and chromatin remodelling proteins during activation of gene expression.
Kistanova
E
E
Department of Medicine, Section of Molecular Genetics, Cardiovascular Institute, Boston University School of Medicine, Center for Advanced Biomedical Research, 700 Albany Street, W-509 Boston, MA 02118-2394, USA.
Dell
H
H
Tsantili
P
P
Falvey
E
E
Cladaras
C
C
Hadzopoulou-Cladaras
M
M
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D019556:COS Cells; D002460:Cell Line; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins; D004563:Electrochemistry; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010750:Phosphoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D000596:Amino Acids; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D017931:DNA Primers; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; C403128:MLX protein, human; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors