High impact information on CEP3

• We report the reconstitution of Cbf3p from recombinant proteins and an analysis of its p58Ctf13 and p23Skp1 subunits. p23Skp1 has both G1- and G2-specific functions in yeast and binds to p58Ctf13 and to the essential Cdc4p component of the ubiquitin conjugating complex Scul(Cdc4) [1].
• In S. cerevisiae, the four-protein Cbf3 complex binds to the essential CDEIII region of centromeric DNA to initiate kinetochore assembly [1].
• We propose that coupled activation and destruction link the assembly of Cbf3p to the duplication of centromeres in S phase [1].
• We show that the function of p23Skp1 in Cbf3p is to activate p58Ctf13 by phosphorylation. p58Ctf13 is an unstable protein that is targeted to the proteosome, probably by Scul(Cdc4)-mediated ubiquitination [1].
• The budding yeast SKP1 gene, identified as a dosage suppressor of a known kinetochore protein mutant, encodes an intrinsic 22.3 kDa subunit of CBF3, a multiprotein complex that binds centromere DNA in vitro [2].

Biological context of CEP3

• CEP3 encodes a centromere protein of Saccharomyces cerevisiae [3].
• Three mutants defined a novel essential gene CEP3 [3].
• Overexpression of Ndc10p suppresses the nocodazole sensitivity of plc1 mutants, implying that the association of Plc1p with CBF3 is important for optimal kinetochore function [4].
• Mutations in genes encoding CBF1 and CBF3, proteins that bind to yeast centromeres, interfere with chromosome segregation in vivo [5].
• A complex of proteins (CBF3) that binds specifically to the CDEIII DNA sequence has been isolated by affinity chromatography [6].

Anatomical context of CEP3

• These minichromosomes, when isolated from cep3 cultures, fail to bind bovine microtubules in vitro [3].

Associations of CEP3 with chemical compounds

• Deletion of PLC1, as well as plc1 mutations which abrogate the interaction of Plc1p with the CBF3 complex, results in a higher frequency of minichromosome loss, nocodazole sensitivity, and mitotic delay [4].
• The budding yeast PLC1 gene encodes a homolog of the delta isoform of mammalian phosphoinositide-specific phospholipase C. Here, we present evidence that Plc1p associates with the kinetochore complex CBF3 [4].
• We find that CBF3 is absolutely essential for this attachment but, contrary to previous reports (Hyman, A. A., K. Middleton, M. Centola, T.J. Mitchison, and J. Carbon. 1992. Microtubule-motor activity of a yeast centromere-binding protein complex. Nature (Lond.). 359:533-536) is not sufficient [5].

Physical interactions of CEP3

• Specifically, the Ndc10p component of the centromere DNA-binding CBF3 complex is altered by the glc7-10 mutation; Ndc10p is hyperphosphorylated in glc7-10 extracts [7].
• Consistent with this possibility, we find that CBF3 interacts with Bir1p, the homologue of the passenger protein Survivin [8].

Regulatory relationships of CEP3

• These results demonstrate a novel role for CBF3 in regulating cytokinesis, a role that is reminiscent of passenger proteins [8].
• Specifically, we show that septin ring separation and disassembly is delayed in anaphase, suggesting that CBF3 regulates septin dynamics [8].

Other interactions of CEP3

• Sgt1p is required for assembling the yeast kinetochore complex, CBF3, via activation of Ctf13p [9].
• KAR3-encoded kinesin is a minus-end-directed motor that functions with centromere binding proteins (CBF3) on an in vitro yeast kinetochore [10].
• In this study, we show that inhibiting the assembly of CBF3 causes disorganized septins and defects in cell polarity that give rise to cytokinesis failures [8].
• Only mutations that affect the CBF3 cycle, and not mutants in outer kinetochore subunits, cause defects in septins [8].
• The unstable F-box protein p58-Ctf13 forms the structural core of the CBF3 kinetochore complex [11].

Analytical, diagnostic and therapeutic context of CEP3

• Probing the Saccharomyces cerevisiae centromeric DNA (CEN DNA)-binding factor 3 (CBF3) kinetochore complex by using atomic force microscopy [12].

References