Human T-cell leukemia virus type I Tax protein transactivates RNA polymerase III promoter in vitro and in vivo.
Tax protein of the human T-cell lymphotropic virus type 1 (HTLV-I) is critical for viral replication and is a potent transcriptional activator of viral and cellular polymerase II (pol II) genes. We report here that Tax is able to transactivate a classical pol III promoter, VA-I. In cotransfection experiments, Tax is shown to increase transcription of the VA-I promoter approximately 25-fold. Moreover, Tax is able to activate VA-I transcription when added exogenously to an in vitro transcription reaction. Using Tax affinity column chromatography, we demonstrate that Tax is able to deplete a HeLa cell extract for components required for transcription of VA-I. The transcriptional activity of the Tax-depleted extract can be restored by the 0.6 phosphocellulose fraction. Interestingly, a consensus binding site for cAMP-responsive element binding protein (CREB) is located upstream of the VA-I promoter, and deletion of this element results in the loss of Tax responsiveness. When this CREB binding site is replaced by a Gal-4 binding site, the VA-I promoter can be transactivated by a Gal4-Tax fusion protein. Taken together, these results suggest that Tax may activate pol III and pol II promoter through a similar mechanism involving the CREB activation pathway. It is also possible that Tax affects pol III transcription by direct interaction with a component of the pol III transcriptional machinery.
Piras
G
G
Laboratory of Molecular Virology, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA.
Dittmer
J
J
Radonovich
M F
MF
Brady
J N
JN
D001483:Base Sequence; D001665:Binding Sites; D016384:Consensus Sequence; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D016356:Gene Products, tax / Q000235:genetics*; D006367:HeLa Cells; D015368:Human T-lymphotropic virus 1 / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012320:RNA Polymerase III / Q000235:genetics*; D016415:Sequence Alignment; D015533:Transcriptional Activation
D017362:Cyclic AMP Response Element-Binding Protein; D017931:DNA Primers; D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D012320:RNA Polymerase III