Takada S, Koike K
Department of Gene Research, Cancer Institute.
Nihon Rinsho. 1993 Feb;51(2):364-9.
The X gene product of hepatitis B virus (HBV) has a trans-activation function. The AP-1, AP-2, kappa B-like, and C/EBP-like sequences, and the 26-bp element in HBV enhancer were identified as X-responsive elements. Although the X protein possesses a transcriptional activation domain, it doesn't bind to the X-responsive elements. However, CREB/ATF-2 becomes able to bind to a CRE-related sequence in the 26-bp element once it complexes with X protein. In addition, X protein was shown to have amino acid sequences homologous to the essential domain of Kunitz-type serine protease inhibitors and directly interacted with the protease, tryptase TL2. Results suggest that X protein modulates the tryptase TL2 activity, which may be involved in the proteolytic cleavage of cellular transcription factors.
乙型肝炎病毒（HBV）的X基因产物具有反式激活功能。AP-1、AP-2、κB样和C/EBP样序列以及HBV增强子中的26碱基对元件被确定为X反应元件。虽然X蛋白具有转录激活结构域，但它并不与X反应元件结合。然而，CREB/ATF-2一旦与X蛋白形成复合物，就能够与26碱基对元件中的CRE相关序列结合。此外，X蛋白被证明具有与Kunitz型丝氨酸蛋白酶抑制剂的必需结构域同源的氨基酸序列，并直接与蛋白酶组织蛋白酶TL2相互作用。结果表明，X蛋白调节组织蛋白酶TL2的活性，这可能参与细胞转录因子的蛋白水解切割。
