Augmentation of human T cell leukaemia virus type I Tax transactivation by octamer binding sites.
The human T cell leukaemia virus type I (HTLV-1) Tax protein is an activator of viral and cellular gene expression. Tax does not bind DNA directly, but does interact with cellular DNA binding proteins. These interactions bring Tax to a specific group of promoters and may help to determine the specificity of Tax transactivation. Previous studies have demonstrated that the activity of Tax, when tethered to a given promoter, is enhanced by the presence of adjacent transcription factor binding sites. To examine the specificity of this augmentation, a series of transcription factor binding sites was tested for the ability to enhance the activity of a Gal-Tax fusion protein. The greatest increase in Gal-Tax activity was observed when an octamer binding site was placed adjacent to the Gal4 binding sites. However, the octamer binding site failed to independently function as a Tax responsive element in the absence of an adjacent Tax-tethering element. Oct-2 was not required for augmentation of Gal-Tax activity as this enhancement was observed in BHK-21 cells, which lack Oct-2. The ability of octamer binding sites to augment transcription was specific for Gal-Tax, as compared to other transactivators. Taken together, these results demonstrate that the degree of Tax transactivation can be influenced by the elemental composition of the target promoter.
Marriott
S J
SJ
Division of Molecular Virology, Baylor College of Medicine, Houston, TX 77030, USA. susanm@bcm.tmc.edu
Payne
K
K
Connor
L M
LM
D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D006224:Cricetinae; D004279:DNA, Viral / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D016356:Gene Products, tax / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D015368:Human T-lymphotropic virus 1 / Q000235:genetics*; D006801:Humans; D050813:Octamer Transcription Factor-2; D011401:Promoter Regions, Genetic / Q000235:genetics; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation / Q000235:genetics*
D004279:DNA, Viral; D004268:DNA-Binding Proteins; C052130:GAL4 protein, S cerevisiae; D016356:Gene Products, tax; D050813:Octamer Transcription Factor-2; C058435:POU2F2 protein, human; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors