The eve stripe 2 enhancer employs multiple modes of transcriptional synergy.
Previous studies have provided a detailed model for the regulation of even-skipped (eve) stripe 2 expression in the Drosophila embryo. The bicoid (bcd) regulatory gradient triggers the expression of hunchback (hb); these work synergistically to activate the stripe in the anterior half of the embryo, bcd also coordinates the expression of two repressors, giant (gt) and Kruppel (Kr), which define the anterior and posterior borders of the stripe, respectively. Here, we report the findings of extensive cis- and trans- complementation analyses using a series of defective stripe 2 enhancers in transgenic embryos. This study reaches two primary conclusions. First, the strip 2 enhancer is inherently 'sensitized' for repression by gt. We propose that gt specifies the sharp anterior stripe border by blocking two tiers of transcriptional synergy, cooperative binding to DNA and cooperative contact of bound activators with the transcription complex. Second, we find that the synergistic activity of hb and bcd is 'promiscuous'. For example, a maternally expressed Gal4-Sp1 fusion protein can functionally replace hb in the stripe 2 enhancer. This finding challenges previous proposals for dedicated hb and bcd interactions in the segmentation process.
Arnosti
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DN
Department of Biology, UCSD, La Jolla 92093-0347, USA.
Barolo
S
S
Levine
M
M
Small
S
S
D000818:Animals; D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D004247:DNA / Q000235:genetics; D004268:DNA-Binding Proteins; D004330:Drosophila / Q000196:embryology* / Q000235:genetics*; D029721:Drosophila Proteins; D004742:Enhancer Elements, Genetic; D005260:Female; D018507:Gene Expression Regulation, Developmental; D017344:Genes, Insect; D005816:Genetic Complementation Test; D018398:Homeodomain Proteins / Q000235:genetics*; D007605:Juvenile Hormones / Q000235:genetics; D008297:Male; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D014157:Transcription Factors; D015533:Transcriptional Activation
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D007605:Juvenile Hormones; D014157:Transcription Factors; C052837:eve protein, Drosophila; C061245:hb protein, Drosophila; D004247:DNA