Nature Cell Biology6, 634 - 641 (2004)
Published online: 20 June 2004; | doi:10.1038/ncb1143
Proteolysis-independent regulation of the transcription factor Met4 by a single Lys 48-linked ubiquitin chain
Karin Flick1, Ikram Ouni1, James A. Wohlschlegel2, Chrissy Capati1, W. Hayes McDonald2, 3, John R. Yates 3rd2
& Peter Kaiser1
1
Department of Biological Chemistry, University of California Irvine, Irvine, CA 92697, USA.
2
Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
3
Current address: Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Correspondence should be addressed to Peter Kaiser pkaiser@uci.edu
The ubiquitin ligase SCFMet30 is required for cell cycle progression in budding yeast. The critical function of SCFMet30 is inactivation of the transcriptional activator Met4. Here we show that a single ubiquitin chain is attached to Met4 through lysine at position 163. Inhibition of Met4 ubiquitination by mutating lysine to arginine at this position constitutively activates, but does not stabilize, Met4. This supports a proteolysis-independent role of Cdc34−SCFMet30-catalysed Met4 ubiquitination. Surprisingly, the ubiquitin chain attached to Met4 is linked through Lys 48 in ubiquitin, a ubiquitin chain structure that is usually required for substrate targeting to the 26S proteasome. These results suggest that Lys 48-linked ubiquitin chains can have a regulatory role independent of proteolysis.
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