Regulation of SCF Complex Function

Indiana University, Bloomington IN

Investigators

Abstract

In yeast, a family of protein complexes termed the SCFs (Skp1-Cullin-F-Box) are required for the degradation of cell cycle regulatory proteins, including the cyclins Cln1, Cln2, and Cln3 and the CDK inhibitor Sic1. The inability to degrade either the Cln's or Sic1 alters the normal progression of cells through the cell cycle. SCF complexes also regulate the choice of carbon, nitrogen, and sulfur source of a yeast cell by targeting specific transcription factors for degradation in yeast. SCF complexes act as ubiquitin ligases for the ubiquitin-conjugating enzyme Cdc34. Each SCF complex contains Skp1, Cdc53, and Rbx1. The substrate specificity of each SCF complex is derived from the F-box protein present. SCF associated F-Box proteins include Cdc4, Met30, and Grr1. A major hypothesis of this research is that changes in the abundance of a specific SCF complex lead to changes in the rate of degradation of specific protein substrates. That is, substrates of SCFCdc4 will be more stable under conditions where SCFCdc4 is less abundant. This hypothesis will be tested by determining the in vivo level of SCFCdc4 vs SCFMet30 under conditions requiring specific SCFs. Determinations of the half-life of proteins degraded by the SCFs under different growth conditions will also be made. Mutants that are sensitive to changes in the levels of SCF components will be examined to determine whether they are defective in switching from one SCF to another. Finally, SCF composition will be tested for changes under different growth conditions. The implications of understanding how SCF complexes are regulated are wide ranging. SCF homologs exist in higher eukaryotes and are critical for the degradation of proteins regulating development, cell proliferation, and the stress response. The central hypothesis of this research is that differences in specific SCF levels will occur under repressing and derepressing conditions for amino acids or sulfur. A second hypothesis is that different nutritional conditions will change the level of a specific SCF activity leading to changes in the stability of its substrates.