乙型肝炎病毒基因组中前-X-编码基因启动子序列的确定及转录活性的鉴定

利用长距离精确聚合酶链反应 (LA PCR)扩增慢性乙型肝炎患者血清来源的 5个全长的HBV基因组DNA ,在分析不同克隆之间的序列变异程度时 ,发现所获得的 5个克隆在X区之前可能还存在一个开放读码框架 (ORF) ,长度 16 8bp ,编码 5 6个氨基酸残基(aa) ,并将其暂时命名为前 X(pre X)。为了解前 X编码区上游DNA序列是否具有启动子活性 ,选取翻译起始密码子ATG上游 2 2 5bp的基因片段 ,将其克隆至报告基因表达载体pCAT3中 ,构建pCAT3 前 X promoter表达载体 ,以该质粒转染HepG2细胞 ,用ELISA法检测报告基因编码产物氯霉素乙酰转移酶 (CAT)的表达活性。结果发现 ,质粒 pCAT3 前 X promoter能够指导CAT的表达 ,吸光度 (A值 )是pCAT3的 3 5倍 ,提示pCAT3 前 X promoter中插入的DNA序列具有启动子活性 ,说明这一段基因序列中存在新的启动子区 ,为研究、界定前 X的ORF的存在提供了直接的依据。

IDENTIFICATION OF PRE-X PROMOTER SEQUENCE IN HEPATITIS B VIRUS GENOME AND APPRAISAL OF ITS TRANSCRIPTION ACTIVITY

It was found that pre-X region was present in five clones of hepatitis B virus (HBV) genome from 2 patients with chronic HBV infection. The open reading frame (ORF) consisted of 168 base pair (bp), and could be transslated with the X gene in frame. To investigate the activity of pre-X gene promoter, promoter DNA sequence was amplified from HBV-DNA by polymerase chain reaction (PCR), The amplified product was cloned into pCAT3 vector, The HepG2 cells were transfected by pCAT3-Pre-X-p. The CAT activity was detected by an enzyme-linked immunosorbent assay (ELISA) kit. It was found that pCAT3-Pre-X-p had higher activity of CAT, which was 3.5 fold over that of pCAT3-promoter. This result implicated that pCAT3-Pre-X-p possessed promoter activity.