Nakamura I, Koike K
Department of Gene Research, Cancer Institute, JFCR, Tokyo, Japan.
Virology. 1992 Dec;191(2):533-40. doi: 10.1016/0042-6822(92)90228-h.
The X protein of hepatitis B virus (HBV) is a transactivator to homologous and heterologous viral and cellular transcriptional regulatory elements. One sequence-specific binding protein, whose binding site located from nt 1102 to nt 1117 of HBV DNA, was identified by mobility shift assay and DNase I foot-printing analysis. A CAT assay experiment demonstrated this 16-bp binding site to have a promoter activity in the X gene transcription. The 58-bp DNA fragment (nt 1085 to nt 1142), which contains the above binding site, could be enhanced by the HBV enhancer. Mobility shift assay using the mutated 58-bp DNA fragments as probes, showed that the mutation, which damaged the palindrome structure between nt 1105 and nt 1112, resulted in loss of the binding activity. This mutation also remarkably reduced the promoter activity. The binding site differed from the target sequences of known transcriptional factors. This factor was thus concluded to be a binding protein to the X gene promoter (X-PBP) of HBV. A homology search demonstrated the binding site to be highly homologous to the promoter elements of human laminin receptor (2H5epitope) and lipoprotein receptor-related protein (LRP) genes.
乙型肝炎病毒（HBV）的X蛋白是一种对同源和异源病毒及细胞转录调控元件起反式激活作用的蛋白。通过凝胶迁移试验和DNase I足迹分析，鉴定出一种序列特异性结合蛋白，其结合位点位于HBV DNA的第1102至1117核苷酸处。一项氯霉素乙酰转移酶（CAT）分析实验表明，这个16个碱基对的结合位点在X基因转录中具有启动子活性。包含上述结合位点的58个碱基对的DNA片段（第1085至1142核苷酸）可被HBV增强子增强。以突变的58个碱基对DNA片段为探针进行凝胶迁移试验，结果显示，破坏第1105至1112核苷酸之间回文结构的突变导致结合活性丧失。这种突变也显著降低了启动子活性。该结合位点不同于已知转录因子的靶序列。因此得出结论，该因子是一种HBV X基因启动子结合蛋白（X-PBP）。同源性搜索表明，该结合位点与人层粘连蛋白受体（2H5表位）和脂蛋白受体相关蛋白（LRP）基因的启动子元件高度同源。
