Cdc53 is a scaffold protein for multiple Cdc34/Skp1/F-box protein complexes that regulate cell division and methionine biosynthesis in yeast

Abstract

In budding yeast, ubiquitination of the cyclin-dependent kinase (Cdk) inhibitor Sic1 is catalyzed by the E2 ubiquitin conjugating enzyme Cdc34 in conjunction with an E3 ubiquitin ligase complex composed of Skp1, Cdc53 and the F-box protein, Cdc4 (the SCF Cdc4 complex). Skp1 binds a motif called the F-box and in turn F-box proteins appear to recruit specific substrates for ubiquitination. We find that Skp1 interacts with Cdc53 in vivo, and that Skp1 bridges Cdc53 to three different F-box proteins, Cdc4, Met30, and Grr1. Cdc53 contains independent binding sites for Cdc34 and Skp1 suggesting it functions as a scaffold protein within an E2/E3 core complex. F-box proteins show remarkable functional specificity in vivo: Cdc4 is specific for degradation of Sic1, Grr1 is specific for degradation of the G 1 cyclin Cln2, and Met30 is specific for repression of methionine biosynthesis genes. In contrast, the Cdc34-Cdc53-Skp1 E2/E3 core complex is required for all three functions. Combinatorial control of SCF complexes may provide a basis for the regulation of diverse cellular processes.

Comprehensive Identification of Cell Cycle–regulated Genes of the YeastSaccharomyces cerevisiaeby Microarray Hybridization

“…Data supporting this idea are that Met30p is involved in cell cycle regulation as an F-box protein that targets Swe1 for degradation (Kaiser et al, 1998;Patton et al, 1998). SWE1 transcription is cell Figure 8.…”

Differential interaction of plakoglobin and β-catenin with the ubiquitin-proteasome system

“…This protein contains two main domains, an F-box motif that binds to Skp1 and enables its assembly with the Skp1/Cul1 complex, and the WD domain that speci®cally binds to the target protein (for reviews see Hershko and Ciechanover, 1998;Ciechanover, 1998;Elledge and Harper, 1998). Cdc53/Cul1 interacts with the E2 ubiquitin-conjugating enzyme that functions in conjunction with the Skp1-b-TrCP complex to link ubiquitin to lysine residues in the target protein (Patton et al, 1998). The importance of b-TrCP in regulating various signaling pathways, by controlling speci®c protein turnover, was recently highlighted in studies demonstrating that b-TrCP and its Drosophila homolog Slimb regulate three di erent signaling pathways (see for review Maniatis, 1999); namely, NF-kB, Wnt/ Wingless and Hedgehog (Yaron et al, 1998;Jiang and Struhl, 1998).…”

Two F‐box/WD‐repeat proteins Pop1 and Pop2 form hetero‐ and homo‐complexes together with cullin‐1 in the fission yeast SCF (Skp1‐Cullin‐1‐F‐box) ubiquitin ligase

“…Proteins were detected with immunoblotting using anti-HA antibody (upper panel), anti-myc antibody (lanes 1-4 of the lower panel) or anti-GST antibody (lanes 5-7 of the lower panel). It is proposed that SCF consists of multiple forms, in which different F-box proteins form distinct SCF complexes, and that each SCF with different F-box proteins regulates the stability of a subset of various substrates in a manner which is dependent on each Fbox protein associated (combinatorial control, Patton et al 1998a). There are several F-box-containing proteins besides Pop1 and Pop2 in the fission yeast genome (K.K., unpublished observation), and thus a similar regulation might be operational in fission yeast SCF.…”

“…SCF Cdc4 and SCF Skp2 ). Cdc53 acts as a scaffold for the SCF complex (Patton et al 1998a) and is also conserved. Furthermore, Cdc53 comprises a large protein family called cullin (Cdc53 is a cullin-1 homologue and humans have at least six cullin members, Kipreos et al 1996).…”