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Molecular and Cellular Biology, September 2001, p. 6292-6311, Vol. 21, No. 18
The Rockefeller University, New York, New
York 10021
Received 1 May 2001/Returned for modification 7 June 2001/Accepted 25 June 2001
Different G1 cyclins confer functional specificity to
the cyclin-dependent kinase (Cdk) Cdc28p in budding yeast. The Cln3p G1 cyclin is localized primarily to the nucleus, while
Cln2p is localized primarily to the cytoplasm. Both binding to Cdc28p
and Cdc28p-dependent phosphorylation in the C-terminal region of Cln2p are independently required for efficient nuclear depletion of Cln2p,
suggesting that this process may be physiologically regulated. The
accumulation of hypophosphorylated Cln2 in the nucleus is an
energy-dependent process, but may not involve the RAN GTPase. Phosphorylation of Cln2p is inefficient in small newborn cells obtained
by elutriation, and this lowered phosphorylation correlates with
reduced Cln2p nuclear depletion in newborn cells. Thus, Cln2p may have
a brief period of nuclear residence early in the cell cycle. In
contrast, the nuclear localization pattern of Cln3p is not influenced
by Cdk activity. Cln3p localization requires a bipartite nuclear
localization signal (NLS) located at the C terminus of the protein.
This sequence is required for nuclear localization of Cln3p and is
sufficient to confer nuclear localization to green fluorescent protein
in a RAN-dependent manner. Mislocalized Cln3p, lacking the NLS, is much
less active in genetic assays specific for Cln3p, but more active in
assays normally specific for Cln2p, consistent with the idea that Cln3p
localization explains a significant part of Clnp functional specificity.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.18.6292-6311.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Mechanisms Controlling Subcellular Localization of
the G1 Cyclins Cln2p and Cln3p in Budding Yeast
and
*
Corresponding author. Mailing address: The Rockefeller
University, 1230 York Ave., New York, NY 10021. Phone: (212) 327-7686. Fax: (212) 327-7193. E-mail:
fcross{at}rockvax.rockefeller.edu.
Present address: Rhodes College, Memphis, TN 38112.
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