Interaction of bovine leukemia virus transactivator Tax with bZip proteins.
The bovine leukemia virus transactivator, BLV Tax, augments transcription from three imperfect 21-bp repeats in the viral transcriptional regulatory region. Each BLV 21-bp repeat contains a cAMP response element (CRE) in the center and unique 5' and 3' neighboring sequences which are crucial for the transcriptional activation by BLV Tax. Here we describe the interactions of recombinant BLV Tax with cellular bZip proteins. The recombinant BLV Tax, tagged at the carboxy terminus with a hexahistidine extension, was prepared by solubilization in 6 M guanidine hydrochloride and renaturation on the Ni(2+)-chelating Sepharose gel matrix. The renatured BLV TaxH6 activates the BLV LTR when introduced into HeLa cells by scrape loading. Furthermore, the purified BLV TaxH6 enhances binding of members of the CREB/ATF family of bZip proteins to CRE motifs by interacting with their bZip domains in vitro. Chemical cross-linking indicates that dimerization of bZip proteins such as CREB becomes greatly facilitated in the presence of BLV Tax. These results suggest that BLV Tax interacts directly with CREB/ATF-like factors to activate viral mRNA transcription.
Boros
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Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D002417:Cattle; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017931:DNA Primers; D004279:DNA, Viral / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D051790:G-Box Binding Factors; D016356:Gene Products, tax / Q000378:metabolism*; D006801:Humans; D001909:Leukemia Virus, Bovine / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D012091:Repetitive Sequences, Nucleic Acid; D015682:Retroviridae Proteins, Oncogenic / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors
D050976:Basic-Leucine Zipper Transcription Factors; D017362:Cyclic AMP Response Element-Binding Protein; D017931:DNA Primers; D004279:DNA, Viral; D004268:DNA-Binding Proteins; D051790:G-Box Binding Factors; D016356:Gene Products, tax; D015682:Retroviridae Proteins, Oncogenic; D015534:Trans-Activators; D014157:Transcription Factors; C059786:transactivator protein p38(tax)