The yeast Cln3 protein is an unstable activator of Cdc28.
The Cln3 cyclin homolog of Saccharomyces cerevisiae functions to promote cell cycle START for only a short time following its synthesis. Cln3 protein is highly unstable and is stabilized by C-terminal truncation. Cln3 binds to Cdc28, a protein kinase catalytic subunit essential for cell cycle START, and Cln3 instability requires Cdc28 activity. The long functional lifetime and the hyperactivity of C-terminally truncated Cln3 (Cln3-2) relative to those of full-length Cln3 are affected by mutations in CDC28: the functional lifetime of Cln3-2 is drastically reduced by the cdc28-13 mutation at the permissive temperature, and the cdc28-4 mutation at the permissive temperature completely blocks the function of Cln3-2 while only partially reducing the function of full-length Cln3. Thus, sequences in the C-terminal third of Cln3 might help stabilize functional Cdc28-Cln3 association, as well as decreasing the lifetime of the Cln3 protein. These and other results strongly support the idea that Cln proteins function to activate Cdc28 at START.
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Rockefeller University, New York, New York 10021.
Blake
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D017489:CDC28 Protein Kinase, S cerevisiae / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002453:Cell Cycle; D016213:Cyclins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D005656:Fungal Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D005800:Genes, Fungal; D015151:Immunoblotting; D016296:Mutagenesis; D010957:Plasmids; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins
C079895:CLN3 protein, S cerevisiae; D016213:Cyclins; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D017489:CDC28 Protein Kinase, S cerevisiae; C074532:Cln3-Cdc28 kinase complex, S cerevisiae