Klemperer N, Ward J, Evans E, Traktman P
Department of Cell Biology and Anatomy, Cornell University Medical College, New York, New York 10021, USA.
J Virol. 1997 Dec;71(12):9285-94. doi: 10.1128/JVI.71.12.9285-9294.1997.
The product of the vaccinia virus I1 gene was characterized biochemically and genetically. This 35-kDa protein is conserved in diverse members of the poxvirus family but shows no homology to nonviral proteins. We show that recombinant I1 binds to both single-stranded and double-stranded DNA in a sequence-nonspecific manner in an electrophoretic mobility shift assay. The protein is expressed at late times during infection, and approximately 700 copies are encapsidated within the virion core. To determine the role of the I1 protein during the viral life cycle, a inducible viral recombinant in which the I1 gene was placed under the regulation of the Escherichia coli lac operator/repressor was constructed. In the absence of isopropyl-beta-D-thiogalactopyranoside, plaque formation was abolished and yields of infectious, intracellular virus were dramatically reduced. Although all phases of gene expression and DNA replication proceeded normally during nonpermissive infections, no mature virions were produced. Electron microscopic analysis confirmed the absence of mature virion assembly but revealed that apparently normal immature virions accumulated. Thus, I1 is an encapsidated DNA-binding protein required for the latest stages of vaccinia virion morphogenesis.
对痘苗病毒I1基因的产物进行了生化和遗传学特征分析。这种35 kDa的蛋白质在痘病毒家族的不同成员中保守，但与非病毒蛋白无同源性。我们发现在电泳迁移率变动分析中，重组I1以序列非特异性方式与单链和双链DNA结合。该蛋白在感染后期表达，约700个拷贝被包装在病毒粒子核心内。为确定I1蛋白在病毒生命周期中的作用，构建了一种诱导型病毒重组体，其中I1基因置于大肠杆菌乳糖操纵子/阻遏物的调控之下。在没有异丙基-β-D-硫代半乳糖苷的情况下，噬斑形成被消除，感染性细胞内病毒的产量显著降低。尽管在非允许感染期间基因表达和DNA复制的所有阶段均正常进行，但未产生成熟病毒粒子。电子显微镜分析证实没有成熟病毒粒子组装，但显示明显正常的未成熟病毒粒子积累。因此，I1是痘苗病毒粒子形态发生最后阶段所需的一种被包装的DNA结合蛋白。
