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Mol. Cell. Biol., 02 1995, 731-741, Vol 15, No. 2
J Yaglom, MH Linskens, S Sadis, DM Rubin, B Futcher and D Finley
Cln3 cyclin of the budding yeast Saccharomyces cerevisiae is a key
regulator of Start, a cell cycle event in G1 phase at which cells become
committed to division. The time of Start is sensitive to Cln3 levels, which
in turn depend on the balance between synthesis and rapid degradation. Here
we report that the breakdown of Cln3 is ubiquitin dependent and involves
the ubiquitin-conjugating enzyme Cdc34 (Ubc3). The C-terminal tail of Cln3
functions as a transferable signal for degradation. Sequences important for
Cln3 degradation are spread throughout the tail and consist largely of PEST
elements, which have been previously suggested to target certain proteins
for rapid turnover. The Cln3 tail also appears to contain multiple
phosphorylation sites, and both phosphorylation and degradation of Cln3 are
deficient in a cdc28ts mutant at the nonpermissive temperature. A point
mutation at Ser-468, which lies within a Cdc28 kinase consensus site,
causes approximately fivefold stabilization of a Cln3-beta- galactosidase
fusion protein that contains a portion of the Cln3 tail and strongly
reduces the phosphorylation of this protein. These data indicate that the
degradation of Cln3 involves CDC28-dependent phosphorylation events.
Copyright © 1995, American Society for Microbiology
p34Cdc28-mediated control of Cln3 cyclin degradation
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115.
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