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Molecular and Cellular Biology, September 1998, p. 5010-5020, Vol. 18, No. 9
Department of Biological Sciences, Columbia
University, New York, New York 10027
Received 30 April 1998/Returned for modification 2 June
1998/Accepted 9 June 1998
Vertebrate poly(A) polymerase (PAP) contains a catalytic domain and
a C-terminal Ser-Thr-rich regulatory region. Consensus and nonconsensus
cyclin-dependent kinase (cdk) sites are conserved in the Ser-Thr-rich
region in vertebrate PAPs. PAP is phosphorylated by cdc2-cyclin B on
these sites in vitro and in vivo and is inactivated by
hyperphosphorylation in M-phase cells, when cdc2-cyclin B is active. In
the experiments described here, we undertook a genetic approach in
chicken DT40 cells to study the function of PAP phosphorylation. We
found that PAP is highly conserved in chicken and is
essential in DT40 cells. While cells could tolerate reduced levels of
PAP, even modest overexpression of either wild-type PAP or a mutant PAP
with two consensus cdk sites mutated (cdk
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Copyright © 1998, American Society for Microbiology. All rights reserved.
Deregulation of Poly(A) Polymerase Interferes with Cell
Growth
and
PAP) was highly
deleterious and at a minimum resulted in reduced growth rates.
Importantly, cells that expressed cdk
PAP had a
significantly lower growth rate than did cells that expressed similar
levels of wild-type PAP, which was reflected in increased accumulation
of cells in the G0-G1 phase of the cell cycle.
We propose that the lower growth rate is due to the failure of
hyperphosphorylation and thus M-phase inactivation of cdk
PAP.
*
Corresponding author. Mailing address: Department of
Biological Sciences, Columbia University, 1212 Amsterdam Ave., New
York, NY 10027. Phone: (212) 854-4647. Fax: (212) 865-8462. E-mail: jlm2{at}columbia.edu.
Present address: Dana-Farber Cancer Institute, Harvard Medical
School, Boston, MA 02115.
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