Avian retroviral long terminal repeats bind CCAAT/enhancer-binding protein.
DNA-protein interactions involving enhancer and promoter sequences within the U3 regions of several avian retroviral long terminal repeats (LTRs) were studied by DNase I footprinting. The rat CCAAT/enhancer-binding protein, C/EBP, bound to all four viral LTRs examined. The Rous sarcoma virus binding site corresponded closely to the 5' limit of the LTR enhancer; nucleotides -225 to -188 were protected as a pair of adjacent binding domains. The Fujinami sarcoma virus LTR bound C/EBP at a single site at nucleotides -213 to -195. C/EBP also bound to the promoter region of the enhancerless Rous-associated virus-0 LTR at nucleotides -77 to -57. The avian myeloblastosis virus LTR bound C/EBP at three sites: nucleotides -262 to -246, -154 to -134, and -55 to -39. We have previously observed binding of C/EBP to an enhancer in the gag gene of avian retroviruses. A heat-treated nuclear extract from chicken liver bound to all of the same retroviral sequences as did C/EBP. Alignment of the avian retroviral binding sequences with the published binding sites for C/EBP in two CCAAT boxes and in the simian virus 40, polyoma, and murine sarcoma virus enhancers suggested TTGNNGCTAATG as a consensus sequence for binding of C/EBP. When two bases of this consensus sequence were altered by site-specific mutagenesis of the Rous sarcoma virus LTR, binding of the heat-stable chicken protein was eliminated.
Ryden
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Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218.
Beemon
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D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins; D004279:DNA, Viral / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D008969:Molecular Sequence Data; D012091:Repetitive Sequences, Nucleic Acid; D012190:Retroviridae / Q000235:genetics* / Q000378:metabolism
D022762:CCAAT-Enhancer-Binding Proteins; D004279:DNA, Viral; D004268:DNA-Binding Proteins