ASF-2: a factor that binds to the cauliflower mosaic virus 35S promoter and a conserved GATA motif in Cab promoters.
We have used nuclear extracts prepared from tobacco leaf tissue to characterize a factor binding site, designated as-2 (activating sequence-2), at the -100 region of the cauliflower mosaic virus 35S promoter. The activity of this factor, called ASF-2 (activating sequence factor-2), is not detected in tobacco root extracts. as-2 includes two GT motifs with sequence homology to the SV40 enhancer core A element and the Box II element of pea rbcS. Nevertheless, oligomers of these sequence elements do not compete for ASF-2 binding in gel retardation assays, indicating that the GT motifs may not be involved. Methylation interference studies identify two guanines (G93 and G98) that are required for interaction with ASF-2. Sequences surrounding these two critical guanines display homologies to a GATA repeat conserved among several light-responsive promoters. One such sequence from a petunia Cab promoter is able to compete with as-2 for factor binding. In transgenic plants, a tetramer of as-2 is able to confer leaf expression when fused 5' to the -90 derivative of the 35S promoter. The expression is not dependent on light and, thus, the as-2 tetramer does not function as a light-responsive element in this context. Histochemical localization of the reporter gene product suggests that the as-2 tetramer directs expression in trichomes, vascular elements, and epidermal and mesophyll cells.
Lam
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Laboratory of Plant Molecular Biology, Rockefeller University, New York 10021-6399.
Chua
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NH
D001483:Base Sequence; D001937:Brassica / Q000382:microbiology*; D004279:DNA, Viral / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry*; D005786:Gene Expression Regulation; D008969:Molecular Sequence Data; D009029:Mosaic Viruses / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D011401:Promoter Regions, Genetic; D012689:Sequence Homology, Nucleic Acid
D004279:DNA, Viral; D004268:DNA-Binding Proteins