The cellular content of Cdc25p, the Ras exchange factor in Saccharomyces cerevisiae, is regulated by destabilization through a cyclin destruction box.
The Cdc25p and Sdc25p proteins were the first members of the family of guanine nucleotide exchange factors to be identified. These proteins promote the formation of active Ras-GTP complex from inactive Ras-GDP complex by exchange of GDP for GTP. Therefore Cdc25p which is the main positive regulator of Ras, regulates through Ras the activity of adenylate cyclase in Saccharomyces cerevisiae. The amino-terminal part of Cdc25p has a sequence similar to the cyclin destruction box (CDB) of mitotic cyclins. This sequence has been reported to be required for ubiquitin-dependent proteolysis. In this study we show that Cdc25p is an unstable polypeptide with a half-life of 15-20 min. Its instability depends upon the presence of the CDB which can also confer instability to other proteins. Degradation of Cdc25p and CDB containing beta-galactosidase was found to be independent of various cell cycle arrest points. The fast degradation of Cdc25p opens the possibility that Ras and the cAMP cascade in yeast are directly modulated by the cellular content of the guanine nucleotide exchange factor rather than variation in activity or localization control.
Kaplon
T
T
Institut de Génétique et Microbiologie, CNRS URA 1354, Université Paris XI, Orsay, France.
Jacquet
M
M
D000595:Amino Acid Sequence; D001483:Base Sequence; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D017931:DNA Primers; D005455:Fluorescent Antibody Technique; D019204:GTP-Binding Proteins / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010749:Phosphoprotein Phosphatases / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D017354:Point Mutation; D011994:Recombinant Proteins / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D001616:beta-Galactosidase / Q000378:metabolism; D020666:ras-GRF1
D018797:Cell Cycle Proteins; D016213:Cyclins; D017931:DNA Primers; D011994:Recombinant Proteins; D020666:ras-GRF1; D003513:Cycloheximide; D010749:Phosphoprotein Phosphatases; D001616:beta-Galactosidase; D019204:GTP-Binding Proteins