Greeve J, Hartwig D, Windler E, Greten H
Medizinische Klinik, Universitäts-Krankenhaus Eppendorf, Hamburg, Germany.
Biochimie. 1994;76(12):1209-16. doi: 10.1016/0300-9084(94)90051-5.
Hepatitis delta virus is a satellite of the hepatitis B virus which provides the surface antigen for the viral coat. The genome of the hepatitis delta virus consists of a single-stranded, circular RNA of 1679 nucleotides which forms a rod structure due to a high extent of self homology and which replicates via synthesis of an antigenomic RNA in a rolling circle mechanism similar to plant viroids. The antigenomic RNA contains the open reading frame for the delta-antigen which exists in two isoforms, p24 and p27. The formation of these two isoforms is explained by RNA editing at nucleotide 1012 which changes the stop translation codon UAG at amino acid residue 196 into the codon UGG for tryptophan and extends the open reading frame for the synthesis of p27. In order to investigate whether the editing occurs cotranscriptionally during RNA replication or is a posttranscriptional base modification in the genomic or antigenomic RNA, replication defective deletion mutants of the HDV genome were constructed and expressed in COS-7 cells. Editing was demonstrated in non-replicating fragments of genomic HDV RNA but not in antigenomic HDV RNA fragments. The sequences from nucleotide position 337-1200 of the genomic RNA were sufficient to enable low levels of editing. Editing at position 1012 required the opposite strand of the RNA rod from nucleotide position 337-783. Replicating circular HDV RNA was much more efficiently edited than non-replicating full length genomic HDV RNA. Expression of delta-antigen in trans did not complement the low editing efficiency of replication defective genomic HDV RNA. These results demonstrate posttranscriptional U to C editing in the genomic HDV RNA and exclude misincorporation during HDV RNA replication as the editing mechanism. The minimal structural requirements for HDV RNA editing reside between nucleotide position 337-1200.
丁型肝炎病毒是乙型肝炎病毒的一种卫星病毒，它为病毒衣壳提供表面抗原。丁型肝炎病毒的基因组由一条1679个核苷酸的单链环状RNA组成，由于高度的自我同源性，该RNA形成杆状结构，并通过滚环机制合成反基因组RNA进行复制，这一机制类似于植物类病毒。反基因组RNA包含δ抗原的开放阅读框，δ抗原有两种异构体，即p24和p27。这两种异构体的形成是由于核苷酸1012处的RNA编辑，该编辑将氨基酸残基196处的终止翻译密码子UAG变为色氨酸的密码子UGG，并延长了p27合成的开放阅读框。为了研究这种编辑是在RNA复制过程中发生的共转录过程，还是基因组或反基因组RNA中的转录后碱基修饰，构建了HDV基因组的复制缺陷缺失突变体，并在COS-7细胞中进行表达。在基因组HDV RNA的非复制片段中证实了编辑，但在反基因组HDV RNA片段中未证实。基因组RNA核苷酸位置337 - 1200的序列足以实现低水平的编辑。1012位的编辑需要RNA杆状结构中核苷酸位置337 - 783的反义链。复制性环状HDV RNA的编辑效率比非复制性全长基因组HDV RNA高得多。反式表达δ抗原并不能弥补复制缺陷型基因组HDV RNA的低编辑效率。这些结果证明了基因组HDV RNA中存在转录后U到C的编辑，并排除了HDV RNA复制过程中的错误掺入作为编辑机制。HDV RNA编辑的最小结构要求位于核苷酸位置337 - 1200之间。
