Activity regulation of a Hox protein and a role for the homeodomain in inhibiting transcriptional activation.
Hox proteins are transcription factors that assign positional identities along the body axis of animal embryos. Different Hox proteins have similar DNA-binding functions in vitro and require cofactors to achieve their biological functions. Cofactors can function by enhancement of the DNA-binding specificity of Hox proteins, as has been shown for Extradenticle (Exd). We present results supporting a novel mechanism for Hox cofactor function: regulation of transcriptional activation function. First, we provide evidence that the Hox protein Deformed (Dfd) can interact with simple DNA-binding sites in Drosophila embryos in the absence of Exd, but this binding is not sufficient for transcriptional activation of reporter genes. Secondly, either Dfd or a Dfd-VP16 hybrid mediate much stronger activation in embryos on a Dfd-Exd composite site than on a simple Dfd-binding site, even though the two sites possess similar Dfd-binding affinities. This suggests that Exd is required to release the transcriptional activation function of Dfd independently of Exd enhancement of Dfd-binding affinity on the composite site. Thirdly, transfection assays confirmed that Dfd possesses an activation domain, which is suppressed in a manner dependent on the presence of the homeodomain. The regulation of Hox transcriptional activation functions may underlie the different functional specificities of proteins belonging to this developmental patterning family.
Li
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Department of Biology, University of California, San Diego, La Jolla, CA 92093, USA.
Murre
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McGinnis
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D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004330:Drosophila / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism*; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D015345:Oligonucleotide Probes / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection
D004268:DNA-Binding Proteins; C066676:Dfd protein, Drosophila; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D019476:Insect Proteins; D015345:Oligonucleotide Probes; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C083405:exd protein, Drosophila