The Cln3-Cdc28 kinase complex of S. cerevisiae is regulated by proteolysis and phosphorylation.
In Saccharomyces cerevisiae, several of the proteins involved in the Start decision have been identified; these include the Cdc28 protein kinase and three cyclin-like proteins, Cln1, Cln2 and Cln3. We find that Cln3 is a very unstable, low abundance protein. In contrast, the truncated Cln3-1 protein is stable, suggesting that the PEST-rich C-terminal third of Cln3 is necessary for rapid turnover. Cln3 associates with Cdc28 to form an active kinase complex that phosphorylates Cln3 itself and a co-precipitated substrate of 45 kDa. The cdc34-2 allele, which encodes a defective ubiquitin conjugating enzyme, dramatically increases the kinase activity associated with Cln3, but does not affect the half-life of Cln3. The Cln--Cdc28 complex is inactivated by treatment with non-specific phosphatases; prolonged incubation with ATP restores kinase activity to the dephosphorylated kinase complex. It is thus possible that phosphate residues essential for Cln-Cdc28 kinase activity are added autocatalytically. The multiple post-translational controls on Cln3 activity may help Cln3 tether division to growth.
Tyers
M
M
Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724.
Tokiwa
G
G
Nash
R
R
Futcher
B
B
D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D016203:CDC2 Protein Kinase / Q000378:metabolism; D017489:CDC28 Protein Kinase, S cerevisiae; D002453:Cell Cycle; D004795:Enzyme Stability; D006868:Hydrolysis; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011233:Precipitin Tests; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D014452:Ubiquitins / Q000378:metabolism
D012333:RNA, Messenger; D014452:Ubiquitins; D011494:Protein Kinases; D016203:CDC2 Protein Kinase; D017489:CDC28 Protein Kinase, S cerevisiae; C074532:Cln3-Cdc28 kinase complex, S cerevisiae