Miller R H
Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Gastroenterol Jpn. 1990 Sep;25 Suppl 2:1-5. doi: 10.1007/BF02779920.
In the hepatitis B virus (HBV) genome four long open reading frames (ORFs) have been found that encode the virus core, surface and polymerase proteins as well as a protein that appears to be involved in virus gene expression (X). However, all HBV genomes examined contain two addition ORFs designated ORF5 and ORF6. ORF5 is located on the same strand as the four known viral genes and is 70-100 codons in size. ORF6 is located on the DNA strand complementary to the one that encodes the other virus genes, and is approximately 210 codons in length. Both ORFs are located in the X gene region which corresponds to the 3' terminus of the linear RNA genome. Northern blot analysis identified an X region specific transcript of approximately 0.7 kb. Although this transcript may be the template for the translation of the X gene protein it may also be involved in the expression of the protein encoded by ORF5. The promoter for this transcript may consist, in part, of the 15 residue sequence GCYTGYYTTGCYCGC because this sequence is near the 5' end of the transcript, it is highly conserved among hepadnaviruses, and it contains sequences involved in RNA polymerase binding. Also, the nucleotides within this region of the hepadnavirus genome are capable of forming a stable (G = -18 kcal/mole) hairpin structure. Understanding the organization and gene expression of the X region may be crucial in expanding our knowledge on the biology of HBV.
在乙肝病毒（HBV）基因组中，已发现四个长开放阅读框（ORF），它们编码病毒核心蛋白、表面蛋白和聚合酶蛋白，以及一种似乎参与病毒基因表达的蛋白（X蛋白）。然而，所有检测的HBV基因组都包含另外两个开放阅读框，分别命名为ORF5和ORF6。ORF5与四个已知病毒基因位于同一条链上，大小为70 - 100个密码子。ORF6位于与编码其他病毒基因的DNA链互补的链上，长度约为210个密码子。这两个开放阅读框都位于X基因区域，该区域对应线性RNA基因组的3'末端。Northern印迹分析鉴定出一个约0.7 kb的X区域特异性转录本。虽然这个转录本可能是X基因蛋白翻译的模板，但它也可能参与ORF5编码蛋白的表达。该转录本的启动子可能部分由15个残基的序列GCYTGYYTTGCYCGC组成，因为这个序列靠近转录本的5'端，在嗜肝DNA病毒中高度保守，并且包含与RNA聚合酶结合相关的序列。此外，嗜肝DNA病毒基因组该区域内的核苷酸能够形成一个稳定的（G = -18 kcal/mol）发夹结构。了解X区域的组织和基因表达对于扩展我们对HBV生物学的认识可能至关重要。
