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J. Biol. Chem., Vol. 278, Issue 16, 13819-13828, April 18, 2003
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From the PNUTS, Phosphatase 1 NUclear Targeting Subunit, is a
recently described protein that targets protein phosphatase 1 (PP1) to the nucleus. In the present study, we characterized the biochemical properties of PNUTS. A variety of truncation and site-directed mutants
of PNUTS was prepared and expressed either as glutathione S-transferase fusion proteins in Escherichia
coli or as FLAG-tagged proteins in 293T cells. A 50-amino acid
domain in the center of PNUTS mediated both high affinity PP1 binding
and inhibition of PP1 activity. The PP1-binding domain is related to a
motif found in several other PP1-binding proteins but is distinct in
that Trp replaces Phe. Mutation of the Trp residue essentially
abolished the ability of PNUTS to bind to and inhibit PP1. The central
PP1-binding domain of PNUTS was an effective substrate for protein
kinase A in vitro, and phosphorylation substantially
reduced the ability of PNUTS to bind to PP1 in vitro and
following stimulation of protein kinase A in intact cells. In
vitro RNA binding experiments showed that a C-terminal region
including several RGG motifs and a novel repeat domain rich in His and
Gly interacted with mRNA and single-stranded DNA. PNUTS exhibited
selective binding for poly(A) and poly(G) compared with poly(U) or
poly(C) ribonucleotide homopolymers, with specificity being mediated by
distinct regions within the domain rich in His and Gly and the domain
containing the RGG motifs. Finally, a PNUTS-PP1 complex was isolated
from mammalian cell lysates using RNA-conjugated beads. Together, these studies support a role for PNUTS in protein kinase A-regulated targeting of PP1 to specific RNA-associated complexes in the nucleus.
Department of Biochemistry, College of
Natural Sciences and
Department of Molecular and Cellular
Biochemistry, School of Medicine, Kangwon National University,
Chunchon, Kangwon-Do 200-701, Korea and § Laboratory of
Molecular and Cellular Neuroscience, The Rockefeller University,
New York, New York 10021

To whom correspondence may be addressed: Dept. of Biochemistry,
College of Natural Sciences, Kangwon National University, Chunchon,
Kangwon-Do 200-701, Korea. Tel.: 82-33-250-8517; Fax: 82-33-242-0459;
E-mail: ygkwon@kangwon.ac.kr.
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