Kitagawa K: Yeast Project



Yeast Sgt1 function

The kinetochores of S. cerevisiae are relatively simple compared with the large trilaminar structures seen in multicellular eukaryotes. The minimal functional centromere of S. cerevisiae (approximately 125bp) is comprised of three conserved centromere DNA elements (CDEI, II and III). Of these, CDEIII is absolutely essential for centromere function. Four genes - NDC10, CEP3, CTF13, and SKP1 - are essential for viability and encode the components of a multisubunit complex, CBF3, that binds to CDEIII DNA in vitro (Fig. 2, below). Analysis of CDEIII binding activity of CBF3 in vitro suggests that Sgt1 and Skp1 activate Ctf13.

In addition to their roles in the kinetochore, Sgt1 and Skp1 are involved in the ubiquitin-mediated destruction of the cell cycle regulators at the G1/S transition. Sgt1 and Skp1 are componets of SCF (Skp1, Cdc53, F-box protein) ubiquitin ligase complexes that function together with the ubiquitin conjugating enzyme Cdc34 and Rbx1 (RING-finger protein) in the destruction of Sic1, a CDK inhibitor, and G1 cyclins Cln1/Cln2. Within SCF complexes, Skp1 links the ubiquitin ligase catalytic core composed of Cdc53/Cdc34/Rbx1 with various F-box proteins that recognize different substrates through specific protein-protein interaction motifs. The F-box proteins Cdc4 and Grr1 function to recognize Sic1 and Clns, respectively. Genetic and biochemical data implicates SCF complexes in the phosphorylation-dependent ubiquitination of a number of other regulatory proteins in yeast and vertebrates (Fig. 2, below). Currently, it is not known whether a role for Sgt1/Skp1 in SCF complexes is linked with its kinetochore function.

We are employing a series of genetic and biochemical strategies to identify additional interacting gene products, regulators, and potential substrates of Sgt1/Skp1 action in yeast.

Once Sgt1 forms a complex containing Hsp90, Sgt1 is activated to bind to Skp1. By binding to Sgt1, Skp1 is activated to bind to Ctf13.

Fig 2. Model of CBF3 assembly.

Yeast Bub1 function

Will describe in the near future.


Email This Article Email This Article   |   Print Print