Multisite phosphorylation of a CDK inhibitor sets a threshold for the onset of DNA replication

• Published in: Nature (London) Vol. 414; no. 6863; pp. 514 - 521
• Main Authors: Pawson, Tony, Tyers, Mike, Nash, Piers, Tang, Xiaojing, Orlicky, Stephen, Chen, Qinghua, Gertler, Frank B, Mendenhall, Michael D, Sicheri, Frank
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 29.11.2001; Nature Publishing Group
• Subjects: Binding Sites; Biological and medical sciences; Cdc4 protein; Cell Cycle; Cell Cycle Proteins - antagonists & inhibitors; Cell Cycle Proteins - metabolism; Consensus Sequence; Cyclin-Dependent Kinase Inhibitor Proteins; cyclin-dependent kinase inhibitors; Deoxyribonucleic acid; DNA; DNA Replication - physiology; DNA, Fungal - biosynthesis; Enzyme Inhibitors; F-box protein; F-Box Proteins; Fundamental and applied biological sciences. Psychology; Fungal Proteins - antagonists & inhibitors; Fungal Proteins - metabolism; Fungal Proteins - physiology; Molecular and cellular biology; Molecular biology; Phosphorylation; Protein Structure, Tertiary; Proteins; Saccharomyces cerevisiae Proteins; Sic1 protein; Substrate Specificity; Ubiquitin - metabolism; ubiquitin ligase; Ubiquitin-Protein Ligases; ubiquitination
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/35107009

SCF ubiquitin ligases target phosphorylated substrates for ubiquitin-dependent proteolysis by means of adapter subunits called F-box proteins. The F-box protein Cdc4 captures phosphorylated forms of the cyclin-dependent kinase inhibitor Sic1 for ubiquitination in late G1 phase, an event necessary for the onset of DNA replication. The WD40 repeat domain of Cdc4 binds with high affinity to a consensus phosphopeptide motif (the Cdc4 phospho-degron, CPD), yet Sic1 itself has many sub-optimal CPD motifs that act in concert to mediate Cdc4 binding. The weak CPD sites in Sic1 establish a phosphorylation threshold that delays degradation in vivo, and thereby establishes a minimal G1 phase period needed to ensure proper DNA replication. Multisite phosphorylation may be a more general mechanism to set thresholds in regulated protein-protein interactions.