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J. Virol., 08 1995, 4656-4667, Vol 69, No. 8
MK Hibbard and RM Sandri-Goldin
The herpes simplex virus type 1 (HSV-1) immediate-early protein ICP27 is an
essential regulatory protein that localizes to the nuclei of infected
cells. The strong nuclear localization signal (NLS) of ICP27 was identified
recently and shown to reside in the amino-terminal portion of the
polypeptide from residues 110 to 137 (W.E. Mears, V. Lam, and S.A. Rice, J.
Virol. 69:935-947, 1995). There are also two arginine-rich regions directly
succeeding the NLS. The first of these arginine-rich sequences (residues
141 to 151), together with the NLS, has been shown by Mears et al. to form
the nucleolar localization signal. Arginine-rich motifs are common in
domains involved in nuclear localization and RNA binding. To analyze the
role of the arginine-rich regions in ICP27, we constructed stably
transformed cell lines containing ICP27 mutants with deletions of all or
parts of the NLS and arginine-rich regions. We also constructed mutants in
which these regions were replaced with heterologous NLSs or RNA-binding
domains. Characterization of these mutants indicated that the arginine-rich
regions were required but not sufficient for wild-type localization of
ICP27. More importantly, the NLS and arginine-rich regions were also
essential to the function of ICP27. Mutants lacking these sequences were
defective in late gene expression during infection even when ICP27 was
properly localized to the nucleus by substitution of the NLS from simian
virus 40 large T antigen. Further, the defect in late gene expression could
not be overcome by replacement with the highly basic RNA-binding domain of
human immunodeficiency virus type 1 Tat. The deficiency in late gene
expression was independent of ICP27's role in stimulating viral DNA
replication. In addition, localization of the HSV- 1 proteins ICP4, ICP0,
and ICP8 was unaffected by ICP27 mutants in this region. These results
suggest that the arginine-rich regions are required for efficient nuclear
localization and for the regulatory activity of ICP27 involved in viral
late gene expression.
Copyright © 1995, American Society for Microbiology
Arginine-rich regions succeeding the nuclear localization region of the herpes simplex virus type 1 regulatory protein ICP27 are required for efficient nuclear localization and late gene expression
Department of Microbiology and Molecular Genetics, College of Medicine, University of California, Irvine 92717-4025, USA.
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