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Abstract
Post-translational modification of proteins with ubiquitin regulates a variety of eukaryotic cellular processes. Ubiquitin can be conjugated to substrates either as a single moiety (monoubiquitination) or as isopeptide bond-linked chains (polyubiquitination), creating an array of ubiquitin signals. It has been established that monoubiquitination can serve important functions in many biological processes such as the regulation of gene transcription, protein trafficking, and DNA repair. Surprisingly, little is known about the mechanisms by which monoubiquitin signals are produced in the cell. Here, we discuss the potential cellular strategies for generating monoubiquitinated proteins using a few, relatively well characterized examples of monoubiquitinated proteins. These strategies include coupling ubiquitination to low affinity ubiquitin binding, using monoubiquitination-dedicated E2 conjugating enzymes, and restricting ubiquitin chain elongation. Some of these principles may be applicable to protein modifications involving ubiquitin like proteins (UBLs), which often occur in monomeric form.
Acknowledgements
The authors thank members in the lab for stimulating discussions, and Michael Krause (NIDDK) for critical reading of the manuscript.
Declaration of interest
The authors declare no competing financial interests. The authors’ research is supported by the NIH intramural AIDS Targeted Antiviral Program (IATAP) and by the Intramural Research Program of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
Editor: Michael M. Cox