Recruitment of a SUMO isopeptidase to rDNA stabilizes silencing complexes by opposing SUMO targeted ubiquitin ligase activity
- Jason Liang1,2,4,
- Namit Singh1,4,
- Christopher R. Carlson1,
- Claudio P. Albuquerque1,
- Kevin D. Corbett1,2,3 and
- Huilin Zhou1,3
- 1Ludwig Institute for Cancer Research, San Diego Branch, La Jolla, California 92093, USA;
- 2Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, California 92093, USA;
- 3Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, California 92093, USA
- Corresponding authors: huzhou{at}ucsd.edu, kcorbett{at}ucsd.edu
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↵4 These authors contributed equally to this work.
Abstract
Post-translational modification by SUMO (small ubiquitin-like modifier) plays important but still poorly understood regulatory roles in eukaryotic cells, including as a signal for ubiquitination by SUMO targeted ubiquitin ligases (STUbLs). Here, we delineate the molecular mechanisms for SUMO-dependent control of ribosomal DNA (rDNA) silencing through the opposing actions of a STUbL (Slx5:Slx8) and a SUMO isopeptidase (Ulp2). We identify a conserved region in the Ulp2 C terminus that mediates its specificity for rDNA-associated proteins and show that this region binds directly to the rDNA-associated protein Csm1. Two crystal structures show that Csm1 interacts with Ulp2 and one of its substrates, the rDNA silencing protein Tof2, through adjacent conserved interfaces in its C-terminal domain. Disrupting Csm1's interaction with either Ulp2 or Tof2 dramatically reduces rDNA silencing and causes a marked drop in Tof2 abundance, suggesting that Ulp2 promotes rDNA silencing by opposing STUbL-mediated degradation of silencing proteins. Tof2 abundance is rescued by deletion of the STUbL SLX5 or disruption of its SUMO-interacting motifs, confirming that Tof2 is targeted for degradation in a SUMO- and STUbL-dependent manner. Overall, our results demonstrate how the opposing actions of a localized SUMO isopeptidase and a STUbL regulate rDNA silencing by controlling the abundance of a key rDNA silencing protein, Tof2.
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Footnotes
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Supplemental material is available for this article.
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Article published online ahead of print. Article and publication date are is online at http://www.genesdev.org/cgi/doi/10.1101/gad.296145.117.
- Received January 10, 2017.
- Accepted April 10, 2017.
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