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J. Virol., 09 1997, 6381-6389, Vol 71, No. 9
A Webster, IR Leith, J Nicholson, J Hounsell and RT Hay
Preterminal protein (pTP), the protein primer for adenovirus DNA
replication, is processed at two sites by the virus-encoded protease to
yield mature terminal protein (TP). Here we demonstrate that processing to
TP, via an intermediate (iTP), is conserved in all serotypes sequenced to
date; and in determining the sites cleaved in Ad4 pTP, we extend the
previously published substrate specificity of human adenovirus proteases to
include a glutamine residue at P4. Furthermore, using monoclonal antibodies
raised against pTP, we show that processing to iTP and TP are temporally
separated in the infectious cycle, with processing to iTP taking place
outside the virus particles. In vitro and in vivo studies of viral DNA
replication reveal that iTP can act as a template for initiation and
elongation and argue against a role for virus-encoded protease in switching
off DNA replication. Virus DNA with TP attached to its 5' end (TP-DNA) has
been studied extensively in in vitro DNA replication assays. Given that in
vivo pTP-DNA, not TP-DNA, is the template for all but the first round of
replication, the two templates were compared in vitro and shown to have
different properties. Immunofluorescence studies suggest that a region
spanning the TP cleavage site is involved in defining the subnuclear
localization of pTP. Therefore, a likely role for the processing of pTP-
DNA is to create a distinct template for early transcription (TP-DNA),
while the terminal protein moiety, be it TP or pTP, serves to guide the
template to the appropriate subcellular location through the course of
infection.
Copyright © 1997, American Society for Microbiology
Role of preterminal protein processing in adenovirus replication
School of Biological and Medical Science, University of St. Andrews, Fife, Scotland.
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