Overexpression of Arabidopsis thaliana SKP1 homologues in yeast inactivates the Mig1 repressor by destabilising the F-box protein Grr1.
The timed destruction of cell cycle regulatory proteins is of key importance in controlling cell cycle progression in eukaryotes. Recently, Skp1 from yeast (Saccharomyces cerevisiae) was shown to play an important role in the ubiquitin-mediated proteolysis of these proteins via the Skp1-Cdc53-F-box (SCF) pathway. Here we describe the fortuitous cloning of cDNAs for two Skp1 homologues from the plant Arabidopsis thaliana on account of their ability to activate reporter gene expression in yeast directed by the cyt-1 element from the promoter of the Agrobacterium tumefaciens T-cyt gene, which is essential for expression of the gene in plants. This element is strikingly similar in sequence to the binding site for the yeast Migl protein, a transcriptional repressor of genes involved in the utilisation of carbohydrates other than glucose. We report that Mig1 protein binds to the cyt-1 element with similar specificity as a previously described plant nuclear protein factor, and that the cyt-1 element is a target for an unknown yeast transcriptional activator when Mig1 itself is inactivated. Interestingly, our data further indicate that A. thaliana Skp1 inactivates Mig1 by destabilising the yeast F-box protein Grr1, which is required for cyclin degradation and is thus involved in control of the cell cycle, and for glucose-regulated gene repression. Our results suggest that the plant counterpart of yeast Skp1 is probably also instrumental in ubiquitin-mediated proteolysis of specific proteins via an SCF-like pathway.
Schouten
J
J
Institute of Molecular Plant Sciences, Leiden University, Clusius Laboratory, The Netherlands.
de Kam
R J
RJ
Fetter
K
K
Hoge
J H
JH
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics*; D001483:Base Sequence; D015153:Blotting, Western; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000235:genetics*; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000235:genetics*; D044783:F-Box Proteins; D005656:Fungal Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D010957:Plasmids; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014176:Protein Biosynthesis; D012097:Repressor Proteins / Q000235:genetics*; D044786:S-Phase Kinase-Associated Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D044767:Ubiquitin-Protein Ligases
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D044783:F-Box Proteins; D005656:Fungal Proteins; C085976:MIG1 protein, S cerevisiae; D012097:Repressor Proteins; D044786:S-Phase Kinase-Associated Proteins; D029701:Saccharomyces cerevisiae Proteins; C071032:GRR1 protein, S cerevisiae; D044767:Ubiquitin-Protein Ligases