Jarvis D L, Bohlmeyer D A, Garcia A
Department of Entomology, Texas A&M University, College Station 77843.
J Virol. 1992 Dec;66(12):6903-11. doi: 10.1128/JVI.66.12.6903-6911.1992.
Polyhedrin is the major component of the nuclear viral occlusions produced during replication of the baculovirus Autographa californica multicapsid nuclear polyhedrosis virus (AcMNPV). Since viral occlusions are responsible for the horizontal transmission of AcMNPV in nature, the biosynthesis, localization, and assembly of polyhedrin are important events in the viral replication cycle. We recently defined the sequence requirements for nuclear localization and assembly of polyhedrin. In this study, we examined the localization of polyhedrin at different times of infection. The results showed that nuclear localization of polyhedrin becomes more efficient as the occlusion phase of infection progresses. Several different factors were identified that might contribute to this overall effect, including a higher rate of polyhedrin nuclear localization and a higher rate of polyhedrin biosynthesis. We also examined the biosynthesis and processing of polyhedrin in cells infected with an AcMNPV few polyhedra (FP) mutant, which produces smaller numbers of viral occlusions that contain few or no virions. Compared with wild type, the FP mutant produced polyhedrin more slowly and localized it to the nucleus less efficiently at the beginning of the occlusion phase of infection (24 h postinfection). This supported the idea that the efficiency of polyhedrin nuclear localization is tightly coupled to its rate of biosynthesis. It also revealed that expression of the viral 25K gene, which is inactivated in the FP mutant, is directly or indirectly associated with an enhancement of polyhedrin biosynthesis and nuclear localization at the beginning of the occlusion phase of infection. This enhancement effect appears to be necessary to ensure the normal assembly of viral occlusions.
多角体蛋白是杆状病毒苜蓿银纹夜蛾多粒包埋核型多角体病毒（AcMNPV）复制过程中产生的核病毒包涵体的主要成分。由于病毒包涵体负责AcMNPV在自然界中的水平传播，多角体蛋白的生物合成、定位和组装是病毒复制周期中的重要事件。我们最近确定了多角体蛋白核定位和组装的序列要求。在本研究中，我们检测了感染不同时间点多角体蛋白的定位情况。结果表明，随着感染的包涵体形成阶段的推进，多角体蛋白的核定位效率更高。我们确定了几个可能导致这种总体效应的不同因素，包括更高的多角体蛋白核定位率和更高的多角体蛋白生物合成率。我们还检测了感染AcMNPV少多角体（FP）突变体的细胞中多角体蛋白的生物合成和加工情况，该突变体产生的病毒包涵体数量较少，且几乎不含或不含病毒粒子。与野生型相比，FP突变体在感染的包涵体形成阶段开始时（感染后24小时）产生多角体蛋白的速度较慢，且将其定位到细胞核的效率较低。这支持了多角体蛋白核定位效率与其生物合成速率紧密相关的观点。这也揭示了在FP突变体中失活的病毒25K基因的表达，与感染的包涵体形成阶段开始时多角体蛋白生物合成和核定位的增强直接或间接相关。这种增强效应似乎是确保病毒包涵体正常组装所必需的。
