Twenty-one base pair repeat elements influence the ability of a Gal4-Tax fusion protein to transactivate the HTLV-I long terminal repeat.
The Tax1 protein of the human T-cell leukemia virus (HTLV-I) is a 40-kDa positive transactivator of viral gene expression. Tax1 does not bind directly to DNA, but associates indirectly with DNA via cellular transcription factors. To further investigate the activation of HTLV-I transcription by Tax1, a chimeric protein containing Tax1 fused to the DNA binding domain of Gal4 was created (Gal4-Tax). HTLV-I long terminal repeat (LTR) reporter plasmids were constructed in which specific Tax1 responsive elements were replaced with Gal4 binding sites. Cotransfection of Gal4-Tax or Tax1 with HTLV-I LTR reporter constructs containing Gal4 binding sites demonstrated that Gal4 sequences were necessary but not sufficient for maximal activation of the promoter by Gal4-Tax. Sequences surrounding the Gal4 binding sites were important in determining the level of Gal4-Tax activation. Association of Gal4-Tax with promoters which contained six Gal4 binding sites, but which lacked flanking LTR sequences, were weakly transactivated by Gal4-Tax (sevenfold). In contrast, LTR-CAT reporter constructs containing three Gal4 binding sites flanked by two 21 base pair repeat elements demonstrated a ninefold greater response to Gal4-Tax. These results suggest that cellular transcription factors, which bind the 21 base pair repeat elements, influence the ability of Tax1 to function as a transactivator. Furthermore, this effect is not fully explained by the ability of these factors to physically direct Tax1 to the LTR.
Connor
L M
LM
Division of Molecular Virology, Baylor College of Medicine, Houston, Texas 77030.
Oxman
M N
MN
Brady
J N
JN
Marriott
S J
SJ
D000595:Amino Acid Sequence; D001482:Base Composition; D001483:Base Sequence; D001665:Binding Sites; D004279:DNA, Viral; D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D016356:Gene Products, tax / Q000235:genetics* / Q000378:metabolism; D006367:HeLa Cells; D015368:Human T-lymphotropic virus 1 / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D015533:Transcriptional Activation
D004279:DNA, Viral; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D016356:Gene Products, tax; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors