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.
Rockefeller University, New York, New York 10021.
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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