Yu M, Summers J
Department of Cell Biology, University of New Mexico School of Medicine, Albuquerque 87131-5226.
J Virol. 1991 May;65(5):2511-7. doi: 10.1128/JVI.65.5.2511-2517.1991.
Mutations introduced into the capsid gene of duck hepatitis B virus (DHBV) were tested for their effects on viral DNA synthesis and assembly of enveloped viruses. Four classes of mutant phenotypes were observed among a series of deletions of covering the 3' end of the capsid open reading frame. Class I mutant capsids were able to support normal single-stranded and relaxed circular viral DNA synthesis; class II mutant capsids supported normal single-stranded DNA synthesis but not relaxed circular DNA synthesis; class III mutant capsids resembled class II capsids, but viral DNA synthesis was inhibited 5- to 10-fold; and class IV capsids were severely restricted in their ability to support viral DNA synthesis. Class I capsids were assembled into enveloped virions, but class II, III, and IV capsids were not. Viral DNA synthesized inside class II capsids was normal with respect to minus-strand DNA initiation, plus-strand DNA initiation, and circularization of the DNA, but plus strands failed to be elongated to mature 3-kb DNA. The results suggest that a function of the capsid protein specifically required for viral DNA maturation is also required for assembly of nucleocapsids into envelopes. Thus, class II mutants appear to be defective in the appearance of the "packaging signal" for virus assembly (J. Summers and W. Mason, Cell 29:403-415, 1982).
对鸭乙型肝炎病毒（DHBV）衣壳基因中引入的突变进行了测试，以研究其对病毒DNA合成和包膜病毒组装的影响。在一系列覆盖衣壳开放阅读框3'端的缺失突变中，观察到四类突变表型。I类突变衣壳能够支持正常的单链和松弛环状病毒DNA合成；II类突变衣壳支持正常的单链DNA合成，但不支持松弛环状DNA合成；III类突变衣壳与II类衣壳相似，但病毒DNA合成受到5至10倍的抑制；IV类衣壳支持病毒DNA合成的能力受到严重限制。I类衣壳组装成包膜病毒粒子，而II类、III类和IV类衣壳则不能。在II类衣壳内合成的病毒DNA在负链DNA起始、正链DNA起始和DNA环化方面是正常的，但正链未能延伸至成熟的3kb DNA。结果表明，病毒DNA成熟所需的衣壳蛋白功能对于核衣壳组装成包膜也是必需的。因此，II类突变体似乎在病毒组装的“包装信号”出现方面存在缺陷（J. Summers和W. Mason，《细胞》29:403 - 415，1982）。
