The VBP and a1/EBP leucine zipper factors bind overlapping subsets of avian retroviral long terminal repeat CCAAT/enhancer elements.
Two long terminal repeat (LTR) enhancer-binding proteins which may regulate high rates of avian leukosis virus (ALV) LTR-enhanced c-myc transcription during bursal lymphomagenesis have been identified (A. Ruddell, M. Linial, and M. Groudine, Mol. Cell. Biol. 9:5660-5668, 1989). The genes encoding the a1/EBP and a3/EBP binding factors were cloned by expression screening of a lambda gt11 cDNA library from chicken bursal lymphoma cells. The a1/EBP cDNA encodes a novel leucine zipper transcription factor (W. Bowers and A. Ruddell, J. Virol. 66:6578-6586, 1992). The partial a3/EBP cDNA clone encodes amino acids 84 to 313 of vitellogenin gene-binding protein (VBP), a leucine zipper factor that binds the avian vitellogenin II gene promoter (S. Iyer, D. Davis, and J. Burch, Mol. Cell. Biol. 11:4863-4875, 1991). Multiple VBP mRNAs are expressed in B cells in a pattern identical to that previously observed for VBP in other cell types. The LTR-binding activities of VBP, a1/EBP, and B-cell nuclear extract protein were compared and mapped by gel shift, DNase I footprinting, and methylation interference assays. The purified VBP and a1/EBP bacterial fusion proteins bind overlapping but distinct subsets of CCAAT/enhancer elements in the closely related ALV and Rous sarcoma virus (RSV) LTR enhancers. Protein binding to these CCAAT/enhancer elements accounts for most of the labile LTR enhancer-binding activity observed in B-cell nuclear extracts. VBP and a1/EBP could mediate the high rates of ALV and RSV LTR-enhanced transcription in bursal lymphoma cells and many other cell types.
Smith
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CD
Department of Microbiology and Immunology, University of Rochester School of Medicine, New York 14642.
Baglia
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LA
Curristin
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SM
Ruddell
A
A
D000595:Amino Acid Sequence; D000818:Animals; D001354:Avian Leukosis Virus / Q000235:genetics* / Q000378:metabolism*; D030161:Avian Proteins; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D002645:Chickens; D003001:Cloning, Molecular; D017931:DNA Primers; D004279:DNA, Viral / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D003850:Deoxyribonuclease I; D004742:Enhancer Elements, Genetic; D016259:Genes, myc; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D015345:Oligonucleotide Probes; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014819:Vitellogenins / Q000235:genetics
D030161:Avian Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D004279:DNA, Viral; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D015345:Oligonucleotide Probes; D011994:Recombinant Proteins; D014157:Transcription Factors; D014819:Vitellogenins; D003850:Deoxyribonuclease I