Functional Domains within the Nucleus of a Cell Infected with HSV-1

Abstract

HSV‐1 is a nuclear replicating DNA virus capable of establishing both lytic and latent infections in mammalian cells. Expression of the more than 80 HSV genes (the majority of which do not contain introns) requires complex coordination of viral and cellular factors both temporally, at appropriate points during the infectious cycle, and spatially as the virus transcription, replication and DNA packaging factories develop in the cell nucleus. Whilst the HSV genome encodes sufficient proteins to sustain viral DNA replication, it is reliant upon its host cell for RNA polymerase II and RNA processing machinery, in addition to an increasing number of cellular cofactors, for gene expression. As HSV establishes a lytic infection, cellular gene expression and splicing are inhibited as cellular chromatin is displaced and a dramatic reorganisation of the host cell nucleus occurs. The formation of large protein‐rich factories synthesising viral RNA and replicating and packaging the viral genomes is the most striking alteration. In addition to the synthetic factories, large clumps of cellular and viral intron‐containing RNAs accumulate in the nucleus as a result of the inhibition of splicing, at locations which colocalise with splicing factors, but are separate from transcription sites. An essential HSV protein IE63, discussed here, has been identified with a role in the organisation of the nucleus at many levels including replication and transcription site formation, splicing factor organisation and the transport of RNA. This review is a summary of our present understanding of the organisation of the HSV infected cell nucleus, relating viral genomes, RNA, DNA and proteins in the context of the nucleus. However this is a rapidly evolving field and new factors (both viral and cellular) involved in the regulation of these functional domains are constantly being identified. © 1997 by John Wiley & Sons, Ltd.

Herpesvirus Replication Compartments Originate with Single Incoming Viral Genomes

“…HSV-1 has been shown to form a limited number of RCs (15, 16). Taken together with our finding that a limited number of genomes is expressed per cell, we predicted that each RC would originate with a single genome as was previously suggested (9).…”

“…The average number of HSV-1 RCs per cell has been shown to be lower than the number of added infectious units (16). One explanation may be that several viral genomes are needed to establish a functional RC.…”

“…Later, other methods, including in situ hybridization to viral DNA (8, 13, 14), fluorescence-tagged proteins (15), and incorporation of labeled nucleotides (16), were also described. Studies with HSV-1 suggested that the number of RCs early after infection is fewer than the number of infectious units added per cell (multiplicity of infection [MOI]) and these early RCs are distributed as distinct foci within the nucleus (13–16). At later times postinfection, these compartments coalesce to form a single large replication body occupying most of the nuclear space (15, 17).…”

“…At later times postinfection, these compartments coalesce to form a single large replication body occupying most of the nuclear space (15, 17). Early replication sites also colocalize with transcription sites (16), suggesting that only distinct areas inside the nucleus allow initiation of viral replication and expression.…”

Differences in the intracellular localization and fate of herpes simplex virus tegument proteins early in the infection of Vero cells.

“…6) shows that VP16 also specifically localizes to replication compartments in infected cells, while the co-localization of VP16 and VP22a also demonstrates the presence of proteins involved in capsid biosynthesis in these compartments. The characterization of nuclear compartments in cells infected with HSV-1 is a rapidly expanding field with sometimes contradictory findings (Phelan & Clements, 1997). The VP16-immunoreactive compartment identified in this study most closely resembles that seen by previous workers at a similar stage of infection with antibodies to immature capsids (Ward et al, 1996).…”