Jayan Geetha C, Casey John L
Department of Microbiology and Immunology, Georgetown University Medical Center, Washington, DC 20007, USA.
J Virol. 2005 Sep;79(17):11187-93. doi: 10.1128/JVI.79.17.11187-11193.2005.
RNA editing of the hepatitis delta virus (HDV) antigenome at the amber/W site by the host RNA adenosine deaminase ADAR1 is a critical step in the HDV replication cycle. Editing is required for production of the viral protein hepatitis delta antigen long form (HDAg-L), which is necessary for viral particle production but can inhibit HDV RNA replication. The RNA secondary structural features in ADAR1 substrates are not completely defined, but base pairing in the 20-nucleotide (nt) region 3' of editing sites is thought to be important. The 25-nt region 3' of the HDV amber/W site in HDV genotype I RNA consists of a conserved secondary structure that is mostly base paired but also has asymmetric internal loops and single-base bulges. To understand the effect of this 3' region on the HDV replication cycle, mutations that either increase or decrease base pairing in this region were created and the effects of these changes on amber/W site editing, RNA replication, and virus production were studied. Increased base pairing, particularly in the region 15 to 25 nt 3' of the editing site, significantly increased editing; disruption of base pairing in this region had little effect. Increased editing resulted in a dramatic inhibition of HDV RNA synthesis, mostly due to excess HDAg-L production. Although virus production at early times was unaffected by this reduced RNA replication, at later times it was significantly reduced. Therefore, it appears that the conserved RNA secondary structure around the HDV genotype I amber/W site has been selected not for the highest editing efficiency but for optimal viral replication and secretion.
宿主RNA腺苷脱氨酶ADAR1对丁型肝炎病毒（HDV）反基因组在琥珀色/W位点进行的RNA编辑是HDV复制周期中的关键步骤。编辑是产生病毒蛋白丁型肝炎抗原长形式（HDAg-L）所必需的，HDAg-L是病毒颗粒产生所必需的，但会抑制HDV RNA复制。ADAR1底物中的RNA二级结构特征尚未完全明确，但编辑位点3'端20个核苷酸（nt）区域的碱基配对被认为很重要。HDV基因型I RNA中HDV琥珀色/W位点3'端的25 nt区域由一个保守的二级结构组成，该结构大多为碱基配对，但也有不对称内环和单碱基凸起。为了解该3'区域对HDV复制周期的影响，构建了增加或减少该区域碱基配对的突变体，并研究了这些变化对琥珀色/W位点编辑、RNA复制和病毒产生的影响。碱基配对增加，特别是在编辑位点3'端15至nt 25区域，显著增加了编辑；该区域碱基配对的破坏影响不大。编辑增加导致HDV RNA合成显著抑制，主要是由于过量产生HDAg-L。虽然早期病毒产生不受RNA复制减少的影响，但后期病毒产生显著减少。因此，似乎HDV基因型I琥珀色/W位点周围保守的RNA二级结构并非为了最高编辑效率而被选择，而是为了实现最佳的病毒复制和分泌。
