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Virion assembly factories in the nucleus of polyomavirus-infected cells.

ABSTRACT: Most DNA viruses replicate in the cell nucleus, although the specific sites of virion assembly are as yet poorly defined. Electron microscopy on freeze-substituted, plastic-embedded sections of murine polyomavirus (PyV)-infected 3T3 mouse fibroblasts or mouse embryonic fibroblasts (MEFs) revealed tubular structures in the nucleus adjacent to clusters of assembled virions, with virions apparently "shed" or "budding" from their ends. Promyelocytic leukemia nuclear bodies (PML-NBs) have been suggested as possible sites for viral replication of polyomaviruses (BKV and SV40), herpes simplex virus (HSV), and adenovirus (Ad). Immunohistochemistry and FISH demonstrated co-localization of the viral T-antigen (Tag), PyV DNA, and the host DNA repair protein MRE11, adjacent to the PML-NBs. In PML?/? MEFs the co-localization of MRE11, Tag, and PyV DNA remained unchanged, suggesting that the PML protein itself was not responsible for their association. Furthermore, PyV-infected PML?/? MEFs and PML?/? mice replicated wild-type levels of infectious virus. Therefore, although the PML protein may identify sites of PyV replication, neither the observed "virus factories" nor virus assembly were dependent on PML. The ultrastructure of the tubes suggests a new model for the encapsidation of small DNA viruses.

SUBMITTER: Erickson KD

PROVIDER: S-EPMC3320610 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Virion assembly factories in the nucleus of polyomavirus-infected cells.

Erickson Kimberly D KD Bouchet-Marquis Cedric C Heiser Katie K Szomolanyi-Tsuda Eva E Mishra Rabinarayan R Lamothe Benjamin B Hoenger Andreas A Garcea Robert L RL

PLoS pathogens 20120405 4

Most DNA viruses replicate in the cell nucleus, although the specific sites of virion assembly are as yet poorly defined. Electron microscopy on freeze-substituted, plastic-embedded sections of murine polyomavirus (PyV)-infected 3T3 mouse fibroblasts or mouse embryonic fibroblasts (MEFs) revealed tubular structures in the nucleus adjacent to clusters of assembled virions, with virions apparently "shed" or "budding" from their ends. Promyelocytic leukemia nuclear bodies (PML-NBs) have been sugges ...[more]

PMID: 22496654

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Project description:gp41, one of the baculovirus core genes, encodes the only recognized tegument (O-glycosylated) protein of the occlusion-derived virion (ODV) phenotype so far. A previous study using a temperature-sensitive Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) mutant showed that GP41 plays a crucial role in budded virion (BV) formation. However, the precise function of GP41 in the baculovirus replication cycle remains unclear. In this study, AcMNPV GP41 was found to accumulate around the ring zone (RZ) region within the infected nucleus and finally assembled into both BVs and ODVs. Deletion of gp41 from the AcMNPV genome showed that BVs were no longer formed and ODVs were no longer assembled, suggesting the essential role of this gene in baculovirus virion morphogenesis. In infected cells, besides the 42-kDa monomers, dimers and trimers were detected under nonreducing conditions, whereas only trimeric GP41 forms were selectively incorporated into BVs or ODVs. Mutations of all five cysteines in GP41 individually had minor effects on GP41 oligomer formation, albeit certain mutations impaired infectious BV production, suggesting flexibility in the intermolecular disulfide bonding. Single mutations of key leucines within two predicted leucine zipper-like motifs did not interfere with GP41 oligomerization or BV and ODV formation, but double leucine mutations completely blocked oligomerization of GP41 and progeny BV production. In the latter case, the usual subcellular localization, especially RZ accumulation, of GP41 was abolished. The above findings clearly point out a close correlation between GP41 oligomerization and function and therefore highlight the oligomeric state as the functional form of GP41 in the baculovirus replication cycle.IMPORTANCE The tegument, which is sandwiched between the nucleocapsid and the virion envelope, is an important substructure of many enveloped viruses. It is composed of one or more proteins that have important functions during virus entry, replication, assembly, and egress. Unlike another large DNA virus (herpesvirus) that encodes an extensive set of tegument components, baculoviruses very likely exploit the major tegument protein, GP41, to execute functions in baculovirus virion morphogenesis and assembly. However, the function of this O-glycosylated baculovirus tegument protein remains largely unknown. In this study, we identified trimers as the functional structure of GP41 in baculovirus virion morphogenesis and showed that both disulfide bridging and protein-protein interactions via the two leucine zipper-like domains are involved in the formation of different oligomeric states. This study advances our understanding of the unique viral tegument protein GP41 participating in the life cycle of baculoviruses.

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Virion assembly factories in the nucleus of polyomavirus-infected cells.

Publications

Virion assembly factories in the nucleus of polyomavirus-infected cells.

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