Reference: Xie Y, et al. (2007) The Yeast Hex3{middle dot}Slx8 Heterodimer Is a Ubiquitin Ligase Stimulated by Substrate Sumoylation. J Biol Chem 282(47):34176-84

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Abstract


Hex3 and Slx8 are Saccharomyces cerevisiae proteins with important functions in DNA damage control and maintenance of genomic stability. Both proteins have RING domains at their carboxyl termini. Such domains are common in ubiquitin and ubiquitin-like protein ligases (E3s), but little was known about the molecular functions of either protein. In this study, we identified HEX3 as a high-copy suppressor of a temperature-sensitive SUMO protease mutant, ulp1ts, suggesting that it may affect cellular SUMO dynamics. Remarkably, even a complete deletion of ULP1 is strongly suppressed. Hex3 forms a heterodimer with Slx8. We found that the Hex3*Slx8 complex has a robust substrate-specific E3 ubiquitin ligase activity. In this E3 complex, Slx8 appears to bear the core ligase function, with Hex3 strongly enhancing its activity. Notably, SUMO attachment to a substrate stimulates its Hex3*Slx8-dependent ubiquitination, primarily through direct noncovalent interactions between SUMO and Hex3. Our data reveal a novel mechanism of substrate targeting in which sumoylation of a protein can help trigger its subsequent ubiquitination by recruiting a SUMO-binding ubiquitin ligase.

Reference Type
Journal Article
Authors
Xie Y, Kerscher O, Kroetz MB, McConchie HF, Sung P, Hochstrasser M
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