A trans-activator Tax of human T-cell leukemia virus type 1 binds to NF-kappa B p50 and serum response factor (SRF) and associates with enhancer DNAs of the NF-kappa B site and CArG box.
A transcriptional activator of human T-cell leukemia virus type 1 (HTLV-1) activates at least three distinct enhancers: the viral 21-bp enhancer, the NF-kappa B binding site of the IL-2R alpha gene and the CArG box of the c-fos gene. To understand the mechanisms of Tax transactivations of the NF-kappa B enhancer and CArG box, the interactions of Tax protein with their binding factors were analysed. Using a DNA affinity precipitation (DNAP) assay, we found here that Tax associates with the DNA sequences of the NF-kappa B site and CArG box. These Tax associations with enhancers were observed only in the presence of a nuclear factor(s) and were equal to the activating capacities of Tax mutants. To identify the nuclear factor(s), we defined conditions under which no Tax binding to the NF-kappa B binding site and CArG box was detected with a nuclear extract of 293T cells. Under these conditions, transfections with cDNAs of the NF-kappa B p50 and serum response factor (SRF) produced a factor(s) that mediated Tax binding to the NF-kappa B site and the CArG box respectively. Furthermore, purified Tax protein interacted with purified NF-kappa B p50 and purified SRF, indicating their direct bindings. These observations indicate that Tax protein associates with enhancer sequences of the NF-kappa B site and CArG box through NF-kappa B p50 and SRF respectively. Previously we demonstrated that Tax interacts with CREB and CREM proteins that bind to the 21-bp enhancer DNA. These results together suggest that indirect binding of Tax to DNA through each enhancer binding protein is a general mechanism for Tax transactivation of transcription.
Suzuki
T
T
Department of Cellular and Molecular Biology, University of Tokyo, Japan.
Hirai
H
H
Fujisawa
J
J
Fujita
T
T
Yoshida
M
M
D001483:Base Sequence; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D015967:Gene Expression Regulation, Viral; D016356:Gene Products, tax / Q000378:metabolism*; D015368:Human T-lymphotropic virus 1 / Q000235:genetics*; D006801:Humans; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D016328:NF-kappa B / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D011485:Protein Binding; D026362:Serum Response Factor; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D046911:Macromolecular Substances; D016328:NF-kappa B; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D026362:Serum Response Factor