CDC28 phosphorylates Cac1p and regulates the association of chromatin
assembly factor i with chromatin |
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Authors: | Daniel CB Jeffery Naoko Kakusho Zhiying You Marlene Gharib Brandon Wyse Erin Drury Michael Weinreich Pierre Thibault Alain Verreault Hisao Masai Krassimir Yankulov |
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Institution: | 1.Department of Molecular and Cellular Biology;
University of Guelph; Guelph, Ontario, Canada;2.Genome Dynamics Project; Department of Genome
Medicine; Tokyo Metropolitan Institute of Medical Science; Tokyo, Japan;3.Institute for Research in Immunology and
Cancer; Montréal, Canada;4.Van Andel Research Institute, Grand Rapids, MI USA |
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Abstract: | Chromatin Assembly Factor I (CAF-I) plays a key role in the replication-coupled assembly
of nucleosomes. It is expected that its function is linked to the regulation of the cell
cycle, but little detail is available. Current models suggest that CAF-I is recruited to
replication forks and to chromatin via an interaction between its Cac1p subunit and the
replication sliding clamp, PCNA, and that this interaction is stimulated by the kinase
CDC7. Here we show that another kinase, CDC28,
phosphorylates Cac1p on serines 94 and 515 in early S phase and regulates its association
with chromatin, but not its association with PCNA. Mutations in the Cac1p-phosphorylation
sites of CDC28 but not of CDC7 substantially reduce the
in vivo phosphorylation of Cac1p. However, mutations in the putative
CDC7 target sites on Cac1p reduce its stability. The association of
CAF-I with chromatin is impaired in a cdc28–1 mutant and to a
lesser extent in a cdc7–1 mutant. In addition, mutations in the
Cac1p-phosphorylation sites by both CDC28 and CDC7
reduce gene silencing at the telomeres. We propose that this phosphorylation represents a
regulatory step in the recruitment of CAF-I to chromatin in early S phase that is distinct
from the association of CAF-I with PCNA. Hence, we implicate CDC28 in the
regulation of chromatin reassembly during DNA replication. These findings provide novel
mechanistic insights on the links between cell-cycle regulation, DNA replication and
chromatin reassembly. |
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Keywords: | Chromatin Assembly Factor I (CAF-I) Cyclin-Dependent Kinase 8 (CDK8) Cell cycle Dbf4-Dependent Kinase (DDK) Proliferating Cell Nuclear Antigen (PCNA) |
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