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J. Virol., 02 1997, 1124-1132, Vol 71, No. 2
A Phelan, J Dunlop, AH Patel, ND Stow and JB Clements
We have visualized the intracellular localization of herpes simplex virus
(HSV) type 1 replication and transcription sites in infected HeLa cells by
using direct labelling methods. The number of viral transcription foci
increases in a limited way; however, the number of replication sites
increases in a near-exponential manner throughout infection, and both
replication and transcription sites are found buried throughout the nuclear
interior. Simultaneous visualization of viral transcription and replication
foci shows that the two processes colocalize at early times, but at later
times postinfection, there are additional sites committed solely to
replication. This contrasts with the situation in adenovirus-infected cells
in which, throughout replication, sites of transcription are adjacent to
but do not colocalize with sites of viral DNA replication. The data for an
increase in HSV transcription sites suggest an initial phase of replication
of input genomes which are then transcribed. Sites of HSV replication
colocalize with viral DNA replication and packaging proteins but are
largely distinct from the punctate distribution of small nuclear
ribonucleoprotein particles. Very high multiplicities of infection have
shown an upper limit of some 18 viral transcription foci per nucleus,
suggesting cellular constraints on transcription site formation. Use of
virus replication mutants confirms that the labelled foci are sites of
viral RNA and DNA synthesis; in the absence of viral DNA replication
functions, no replication foci and only a limited number of transcription
foci were present. Absence of a packaging function had no apparent effect
on transcription or replication site formation, illustrating that DNA
packaging is not a prerequisite for ongoing DNA synthesis. Further, the
essential HSV protein IE63 is required for efficient replication site
formation at later times postinfection but is not required for
transcription foci formation.
Copyright © 1997, American Society for Microbiology
Nuclear sites of herpes simplex virus type 1 DNA replication and transcription colocalize at early times postinfection and are largely distinct from RNA processing factors
Institute of Virology, University of Glasgow, Scotland.
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