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J. Virol., 02 1995, 935-947, Vol 69, No. 2
WE Mears, V Lam and SA Rice
Previous work has shown that the herpes simplex virus type 1 (HSV-1)
regulatory protein ICP27 localizes to the cell nucleus and that certain
mutant ICP27 polypeptides localize preferentially in nucleoli. To map the
signals in ICP27 which mediate its nuclear localization, we identified the
portions of ICP27 which can direct a cytoplasmic protein, pyruvate kinase
(PK), to nuclei. Our results demonstrate that ICP27 contains multiple
nuclear localization signals (NLSs) that function with differing
efficiencies. First, ICP27 possesses a strong NLS, mapping to residues 110
to 137, which bears similarity to the bipartite NLSs found in Xenopus
laevis nucleoplasmin and other proteins. Second, ICP27 possesses one or
more weak NLSs which map to a carboxyl-terminal portion of the protein
between residues 140 and 512. Our PK-targeting experiments also demonstrate
that ICP27 contains a relatively short sequence, mapping to residues 110 to
152, that can function as a nucleolar localization signal (NuLS). This
signal includes ICP27's strong NLS as well as 15 contiguous residues which
consist entirely of arginine and glycine. This latter sequence is very
similar to an RGG box, a putative RNA-binding motif found in a number of
cellular proteins which are involved in nuclear RNA processing. To confirm
the results of the PK-targeting experiments, we mutated the ICP27 gene by
deleting sequences encoding either the strong NLS or the RGG box. Deletion
of the strong NLS (residues 109 to 138) resulted in an ICP27 molecule that
was only partially defective for nuclear localization, while deletion of
the RGG box (residues 139 to 153) resulted in a molecule that was nuclear
localized but excluded from nucleoli. Recombinant HSV-1s bearing either of
these deletions were unable to replicate efficiently in Vero cells,
suggesting that ICP27's strong NLS and RGG box carry out important in vivo
functions.
Copyright © 1995, American Society for Microbiology
Identification of nuclear and nucleolar localization signals in the herpes simplex virus regulatory protein ICP27
Department of Biochemistry, University of Alberta, Edmonton, Canada.
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