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Journal of Virology, September 1999, p. 7410-7420, Vol. 73, No. 9
Applied Tumor Virology and Institut National
de la Santé et de la Recherche Médicale U375, Deutsches
Krebsforschungszentrum, Heidelberg, Germany
Received 9 April 1999/Accepted 2 June 1999
The parvovirus minute virus of mice NS1 protein is a
multifunctional protein involved in a variety of processes during virus propagation, ranging from viral DNA replication to promoter regulation and cytotoxic action to the host cell. Since NS1 becomes phosphorylated during infection, it was proposed that the different tasks of this
protein might be regulated in a coordinated manner by phosphorylation. Indeed, comparing biochemical functions of native NS1 with its dephosphorylated counterpart showed that site-specific nicking of the
origin and the helicase and ATPase activities are remarkably reduced
upon NS1 dephosphorylation while site-specific affinity of the protein
to the origin became enhanced. As a consequence, the dephosphorylated
polypeptide is deficient for initiation of DNA replication. By adding
fractionated cell extracts to a kinase-free in vitro replication
system, the combination of two protein components containing members of
the protein kinase C (PKC) family was found to rescue the replication
activity of the dephosphorylated NS1 protein upon addition of PKC
cofactors. One of these components, termed HA-1, also stimulated NS1
helicase function in response to acidic lipids but not phorbol esters,
indicating the involvement of atypical PKC isoforms in the modulation
of this NS1 function (J. P. F. Nüesch, S. Dettwiler, R. Corbau, and J. Rommelaere, J. Virol. 72:9966-9977, 1998). The
present study led to the identification of atypical PKC
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
DNA Unwinding Functions of Minute Virus of Mice NS1
Protein Are Modulated Specifically by the Lambda Isoform of Protein
Kinase C
/
as the
active component of HA-1 responsible for the regulation of NS1 DNA
unwinding and replicative functions. Moreover, a target PKC
phosphorylation site was localized at S473 of NS1. By site-directed
mutagenesis, we showed that this residue is essential for NS1 helicase
activity but not promoter regulation, suggesting a possible modulation
of NS1 functions by PKC
phosphorylation at residue S473.
*
Corresponding author. Mailing address: Department of
Applied Tumor Virology Abt F0100 and INSERM U375, Deutsches
Krebsforschungszentrum, Im Neuenheimer Feld 242, D-69120 Heidelberg,
Germany. Phone: (49) 6221 424969. Fax: (49) 6221 424962. E-mail:
jpf.nuesch{at}dkfz-heidelberg.de.
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