Antunović J, Lemieux N, Cromlish J A
Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
Cell Mol Biol Res. 1993;39(5):463-82.
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.
在含有预组装转录起始前复合物的HeLa细胞NTP耗尽提取物中，在细菌中表达的乙肝病毒17 kDa x基因产物以不依赖ATP的方式将人U6启动子激活三到八倍。然而，如果在组装之前添加，HBx会抑制启动子。在瞬时转染分析中观察到的U6转录的HBx依赖性“抑制”以及在体外观察到的反式激活均依赖于上游八聚体元件的存在。HBx通过蛋白质-蛋白质相互作用被整合到含有Oct-1激活结构域的DNA复合物中，并整合到稳定的U6起始前复合物中。这与作为与基础转录机制相互作用的共激活因子的作用一致。我们提出，HBx依赖性的U6转录反式激活和抑制是通过限制起始的转录因子的变化发生的，并提出HBx可能在体内转录调控中具有双重作用。
