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The N-end rule pathway is mediated by a complex of the RING-type Ubr1 and HECT-type Ufd4 ubiquitin ligases

Nature Cell Biology volume 12, pages 1177–1185 (2010)Cite this article

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Abstract

Substrates of the N-end rule pathway are recognized by the Ubr1 E3 ubiquitin ligase through their destabilizing amino-terminal residues. Our previous work showed that the Ubr1 E3 and the Ufd4 E3 together target an internal degradation signal (degron) of the Mgt1 DNA repair protein. Ufd4 is an E3 enzyme of the ubiquitin-fusion degradation (UFD) pathway that recognizes an N-terminal ubiquitin moiety. Here we show that the RING-type Ubr1 E3 and the HECT-type Ufd4 E3 interact, both physically and functionally. Although Ubr1 can recognize and polyubiquitylate an N-end rule substrate in the absence of Ufd4, the Ubr1–Ufd4 complex is more processive in that it produces a longer substrate-linked polyubiquitin chain. Conversely, Ubr1 can function as a polyubiquitylation-enhancing component of the Ubr1–Ufd4 complex in its targeting of UFD substrates. We also found that Ubr1 can recognize the N-terminal ubiquitin moiety. These and related advances unify two proteolytic systems that have been studied separately for two decades.

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Figure 1: The Arg/N-end rule and UFD pathways.
Figure 2: Ubiquitylation of Mgt1 by Ubr1–Ufd4.
Figure 3: Physical interaction between Ubr1 and Ufd4.
Figure 4: Enhancement of ubiquitylation and degradation of Arg/N-end rule substrates by Ufd4.
Figure 5: Ufd4 augments the Arg/N-end rule pathway.
Figure 6: Recognition and synergistic polyubiquitylation of UFD substrates by Ufd4 and Ubr1.

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Acknowledgements

We thank S. Jentsch and A. Toh-e for strains and plasmids; the present and former members of the Varshavsky laboratory, particularly J. Sheng and K. Piatkov, for gifts of plasmids and strains; and O. Batygin for technical assistance. This work was supported by National Institutes of Health grants GM031530, DK039520 and GM085371 (A.V.), and also by grants from the March of Dimes Foundation and the Caltech–City of Hope Biomedical Initiative (A.V.).

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  1. Division of Biology, California Institute of Technology, Pasadena, 91125, California, USA

    Cheol-Sang Hwang, Anna Shemorry & Alexander Varshavsky

  2. Dualsystems Biotech AG, Grabenstrasse 11a, 8952, Schlieren, Switzerland

    Daniel Auerbach

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C.-S.H, A.S., D.A. and A.V. designed experiments. C.-S.H. and A.S. performed the experiments. C.-S.H, A.S. and A.V. wrote the manuscript.

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Correspondence to Alexander Varshavsky.

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Hwang, CS., Shemorry, A., Auerbach, D. et al. The N-end rule pathway is mediated by a complex of the RING-type Ubr1 and HECT-type Ufd4 ubiquitin ligases. Nat Cell Biol 12, 1177–1185 (2010). https://doi.org/10.1038/ncb2121

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