Journal
CELL CYCLE
Volume 9, Issue 21, Pages 4282-4285Publisher
TAYLOR & FRANCIS INC
DOI: 10.4161/cc.9.21.13741
Keywords
ubiquitin; proteasome; yeast; mating type; functional redundancy; SUMO
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Funding
- NIH [GM046904, GM053756]
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As central components of the intricate networks of eukaryotic gene regulation, transcription factors are frequent targets of ubiquitin-dependent proteolysis. A well-known example is the budding yeast MAT alpha 2 (alpha 2) transcriptional repressor, which functions as a master regulator of cell-type determination. Degradation of alpha 2 by the ubiquitin-proteasome system is necessary for a phenotypic switch from one cell type to another. A surprisingly complex set of ubiquitin-protein conjugation mechanisms are involved. One pathway utilizes an integral-membrane ubiquitin ligase (E3) that also functions in endoplasmic reticulum-associated degradation (ERAD). Recently, we showed that a second alpha 2 ubiquitylation pathway uses a heterodimeric E3 that, while able to bind the ubiquitin-like protein SUMO, directly recognizes non-sumoylated alpha 2. Other transcription factors are now also known to be ubiquitylated by multiple mechanisms; as many as a dozen E3s have been implicated in degradation of the human p53 tumor suppressor, for example. We discuss general issues of redundancy and mechanistic variation in protein modification by ubiquitin.
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