Live Cell Microscopy of Murine Polyomavirus Subnuclear Replication Centers

Proteome profiling of polyomavirus nuclear replication centers using iPOND

Polyomaviruses (PyVs) cause diverse diseases in a variety of mammalian hosts. During the life cycle, PyVs recruit nuclear host factors to viral genomes to facilitate replication and transcription. While host factors involved in DNA replication, DNA damage sensing and repair, and cell cycle regulation have been observed to bind PyV DNA, the complete set of viral and host proteins comprising the PyV replisome remains incompletely characterized. Here, the iPOND-MS technique (Isolation of Proteins on Nascent DNA coupled with Mass Spectrometry) was used to identify the proteome bound to murine PyV (MuPyV) DNA immediately following synthesis and 2 hours post-synthesis. Several novel MuPyV DNA interactors were identified on newly synthesized viral DNA (vDNA), including MCM complex members, DNA primase, DNA polymerase alpha, DNA ligase, and replication factor C. Though displaying partial overlap, the host and viral proteins bound to MuPyV DNA 2 hours post-synthesis lacked many of the replication proteins found on newly synthesized vDNA. These data help distinguish between the host factors critical for MuPyV DNA replication and those involved in downstream processing.IMPORTANCEPolyomaviruses are the causative agents of serious diseases in humans, including progressive multifocal leukoencephalopathy (PML), BK virus nephropathy, and Merkel cell carcinoma. The exact mechanisms by which the virus replicates, and which host cell proteins are required, are incompletely characterized. Identifying the host proteins necessary for efficient viral replication in the cell may reveal targets for downstream targets that may suppress viral replication in vivo.

Replication Compartments of Eukaryotic and Bacterial DNA Viruses: Common Themes Between Different Domains of Host Cells

Subcellular organization is essential for life. Cells organize their functions into organelles to concentrate their machinery and supplies for optimal efficiency. Likewise, viruses organize their replication machinery into compartments or factories within their host cells for optimal replicative efficiency. In this review, we discuss how DNA viruses that infect both eukaryotic cells and bacteria assemble replication compartments for synthesis of progeny viral DNA and transcription of the viral genome. Eukaryotic DNA viruses assemble replication compartments in the nucleus of the host cell while DNA bacteriophages assemble compartments called phage nuclei in the bacterial cytoplasm. Thus, DNA viruses infecting host cells from different domains of life share common replication strategies.

Components of the LINC and NPC complexes coordinately target and translocate a virus into the nucleus to promote infection

Nuclear entry represents the final and decisive infection step for most DNA viruses, although how this is accomplished by some viruses is unclear. Polyomavirus SV40 transports from the cell surface through the endosome, the endoplasmic reticulum, and the cytosol from where it enters the nucleus to cause infection. Here we elucidate the nuclear entry mechanism of SV40. Our results show that cytosol-localized SV40 is targeted to the nuclear envelope by directly engaging Nesprin-2 of the linker of nucleoskeleton and cytoskeleton (LINC) nuclear membrane complex. Additionally, we identify the NUP188 subunit of the nuclear pore complex (NPC) as a new Nesprin-2-interacting partner. This physical proximity positions the NPC to capture SV40 upon release from Nesprin-2, enabling the channel to facilitate nuclear translocation of the virus. Strikingly, SV40 disassembles during nuclear entry, generating a viral genome-VP1-VP3 subcomplex that efficiently crosses the NPC to enter the nucleus. Our results reveal how two major nuclear membrane protein complexes are exploited to promote targeting and translocation of a virus into the nucleus.