Replication Compartments of DNA Viruses in the Nucleus: Location, Location, Location

Abstract

DNA viruses that replicate in the nucleus encompass a range of ubiquitous and clinically important viruses, from acute pathogens to persistent tumor viruses. These viruses must co-opt nuclear processes for the benefit of the virus, whilst evading host processes that would otherwise attenuate viral replication. Accordingly, DNA viruses induce the formation of membraneless assemblies termed viral replication compartments (VRCs). These compartments facilitate the spatial organization of viral processes and regulate virus-host interactions. Here, we review advances in our understanding of VRCs. We cover their initiation and formation, their function as the sites of viral processes, and aspects of their composition and organization. In doing so, we highlight ongoing and emerging areas of research highly pertinent to our understanding of nuclear-replicating DNA viruses.

Keywords: DNA replication; DNA virus; biomolecular condensate; nucleus; phase separation; replication center; replication compartment.

Figure 1

Viral replication compartments are the sites of viral genome replication. Immunofluorescence confocal microscope images showing viral replication compartments in a human adenovirus infected bronchial epithelial cell (A), or herpes simplex virus 1-infected foreskin fibroblast (B). The nucleus is visualized by the staining of DNA with DAPI. Viral replication compartments are visualized by the immunostaining of viral single-stranded DNA (ssDNA)-binding proteins DNA binding protein (DBP) or infected-cell protein 8 (ICP8), respectively. The sites of viral DNA replication are visualized by incorporating 5-Ethynyl-2’-deoxyuridine (EdU) into DNA during replication (15 min pulse, 10 µM), and subsequently conjugating fluorophores to EdU in a copper-catalyzed cycloaddition reaction. The outline of the nucleus is shown (dotted line). Scale bar = 10 µm.

Figure 2

Schematic of human adenovirus and herpes simplex virus 1 replication compartments showing elements of compartment sub-structure and proximal virus-induced domains. (A): Partial cross-section of a human adenovirus (HAdV) replication compartment showing virus-induced post-replicative (VIPR) body, single-stranded DNA accumulation site (ssDAS), and peripheral-replicative zone (PRZ). The presence of the viral assembly/packaging protein 52-55K within and proximal to the PRZ is also shown, as is a pIX body, and promyelocytic leukemia protein (PML) track containing the viral early protein E4orf3. (B): Partial cross-section of a herpes simplex virus 1 (HSV-1) replication compartment showing infected cell protein 4 (ICP4) and infected cell protein 8 (ICP8) positive regions within, which are associated with transcription and genome replication, respectively. A virus-induced chaperone enriched (VICE) domain and SSRP1 focus are shown at the outer edge of the replication compartment.