The 17 kDa HBx protein encoded by hepatitis B virus interacts with the activation domains of Oct-1, and functions as a coactivator in the activation and repression of a human U6 promoter.
The hepatitis B virus 17 kDa x gene product expressed in bacteria transactivates a human U6 promoter three- to eightfold in an ATP-independent manner in HeLa cell NTP-depleted extracts containing preassembled transcription preinitiation complexes. However, if added prior to assembly, HBx squelches the promoter. Both the HBx dependent "squelching" of U6 transcription observed in transient transfection analysis, and the transactivation observed in vitro is dependent on the presence of an upstream octamer element. HBx is incorporated via protein-protein interactions into DNA complexes containing the activation domains of Oct-1, and into a stable U6 preinitiation complex. This is consistent with a role as a coactivator interacting with the basal transcription machinery. We propose that the HBx dependent transactivation and repression of U6 transcription occurs by changes in the transcription factor limiting initiation, and propose that HBx may have a dual role in the regulation of transcription in vivo.
Antunović
J
J
Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
Lemieux
N
N
Cromlish
J A
JA
D000255:Adenosine Triphosphate / Q000494:pharmacology; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D051863:Host Cell Factor C1; D006801:Humans; D008957:Models, Genetic; D008969:Molecular Sequence Data; D050811:Octamer Transcription Factor-1; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D012320:RNA Polymerase III / Q000378:metabolism; D017414:Ribonucleoprotein, U4-U6 Small Nuclear / Q000235:genetics*; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation / Q000187:drug effects; D054334:Viral Regulatory and Accessory Proteins
D004268:DNA-Binding Proteins; C497692:HCFC1 protein, human; D051863:Host Cell Factor C1; D050811:Octamer Transcription Factor-1; C494165:POU2F1 protein, human; D017414:Ribonucleoprotein, U4-U6 Small Nuclear; D015534:Trans-Activators; D014157:Transcription Factors; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; D000255:Adenosine Triphosphate; D012320:RNA Polymerase III