Cao Feng, Scougall Catherine A, Jilbert Allison R, Tavis John E
Department of Molecular Microbiology and Immunology, Saint Louis University School of Medicine, 1100 S. Grand Blvd., St. Louis, MO 63104, USA.
J Virol. 2009 Feb;83(3):1368-78. doi: 10.1128/JVI.01263-08. Epub 2008 Nov 12.
The duck hepatitis B virus (DHBV) pregenomic RNA is a bicistronic mRNA encoding the core and polymerase proteins. Thirteen AUGs (C2 to C14) and 10 stop codons (S1 to S10) are located between the C1 AUG for the core protein and the P1 AUG that initiates polymerase translation. We previously found that the translation of the DHBV polymerase is initiated by ribosomal shunting. Here, we assessed the biosynthetic events after shunting. Translation of the polymerase open reading frame was found to initiate at the C13, C14, and P1 AUGs. Initiation at the C13 AUG occurred through ribosomal shunting because translation from this codon was cap dependent but was insensitive to blocking ribosomal scanning internally in the message. C13 and C14 are in frame with P1, and translation from these upstream start codons led to the production of larger isoforms of P. We named these isoforms "pre-P" by analogy to the pre-C and pre-S regions of the core and surface antigen open reading frames. Pre-P was produced in DHBV16 and AusDHBV-infected duck liver and was predicted to exist in 80% of avian hepadnavirus strains. Pre-P was not encapsidated into DHBV core particles, and the viable strain DHBV3 cannot make pre-P, so it is not essential for viral replication. Surprisingly, we found that pre-P is an N-linked glycoprotein that is secreted into the medium of cultured cells. These data indicate that DHBV produces an additional protein that has not been previously reported. Identifying the role of pre-P may improve our understanding of the biology of DHBV infection.
鸭乙型肝炎病毒（DHBV）前基因组RNA是一种双顺反子mRNA，编码核心蛋白和聚合酶蛋白。在核心蛋白的C1 AUG和启动聚合酶翻译的P1 AUG之间，有13个AUG（C2至C14）和10个终止密码子（S1至S10）。我们先前发现，DHBV聚合酶的翻译是通过核糖体跳跃起始的。在此，我们评估了跳跃后的生物合成事件。发现聚合酶开放阅读框的翻译起始于C13、C14和P1 AUG。在C13 AUG处的起始是通过核糖体跳跃发生的，因为从这个密码子开始的翻译依赖于帽子结构，但对在mRNA内部阻断核糖体扫描不敏感。C13和C14与P1在同一阅读框内，从这些上游起始密码子开始的翻译导致产生更大的P同工型。我们将这些同工型类比于核心抗原和表面抗原开放阅读框的前C和前S区域，命名为“前P”。前P在感染DHBV16和澳大利亚DHBV的鸭肝脏中产生，预计存在于80%的禽嗜肝DNA病毒株中。前P没有被包装进DHBV核心颗粒中，并且活病毒株DHBV3不能产生前P，因此它对病毒复制不是必需的。令人惊讶的是，我们发现前P是一种N-连接糖蛋白，可分泌到培养细胞的培养基中。这些数据表明，DHBV产生了一种以前未报道过的额外蛋白。确定前P的作用可能会增进我们对DHBV感染生物学的理解。
