F-box protein specificity for g1 cyclins is dictated by subcellular localization

• Published in: PLoS genetics Vol. 8; no. 7; p. e1002851
• Main Authors: Landry, Benjamin D, Doyle, John P, Toczyski, David P, Benanti, Jennifer A
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.07.2012; Public Library of Science (PLoS)
• Subjects: Biology; Cell cycle; Cell Cycle Checkpoints; Cell Cycle Proteins - genetics; Cell Cycle Proteins - metabolism; Cell Division - genetics; Cyclins; Cyclins - genetics; Cyclins - metabolism; F-Box Proteins - genetics; F-Box Proteins - metabolism; Gene Expression Regulation, Fungal; Kinases; Mutation; Observations; Phosphorylation; Protein Binding; Protein-protein interactions; Proteins; Proteolysis; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Signal Transduction; SKP Cullin F-Box Protein Ligases - genetics; SKP Cullin F-Box Protein Ligases - metabolism; Substrate Specificity; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism; Yeast; United States
• ISSN: 1553-7404; 1553-7390; 1553-7404
• DOI: 10.1371/journal.pgen.1002851

Levels of G1 cyclins fluctuate in response to environmental cues and couple mitotic signaling to cell cycle entry. The G1 cyclin Cln3 is a key regulator of cell size and cell cycle entry in budding yeast. Cln3 degradation is essential for proper cell cycle control; however, the mechanisms that control Cln3 degradation are largely unknown. Here we show that two SCF ubiquitin ligases, SCF(Cdc4) and SCF(Grr1), redundantly target Cln3 for degradation. While the F-box proteins (FBPs) Cdc4 and Grr1 were previously thought to target non-overlapping sets of substrates, we find that Cdc4 and Grr1 each bind to all 3 G1 cyclins in cell extracts, yet only Cln3 is redundantly targeted in vivo, due in part to its nuclear localization. The related cyclin Cln2 is cytoplasmic and exclusively targeted by Grr1. However, Cdc4 can interact with Cdk-phosphorylated Cln2 and target it for degradation when cytoplasmic Cdc4 localization is forced in vivo. These findings suggest that Cdc4 and Grr1 may share additional redundant targets and, consistent with this possibility, grr1Δ cdc4-1 cells demonstrate a CLN3-independent synergistic growth defect. Our findings demonstrate that structurally distinct FBPs are capable of interacting with some of the same substrates; however, in vivo specificity is achieved in part by subcellular localization. Additionally, the FBPs Cdc4 and Grr1 are partially redundant for proliferation and viability, likely sharing additional redundant substrates whose degradation is important for cell cycle progression.