Westerbeck JW, Pasupala N, Guillotte M, Szymanski E, Matson BC, Esteban C, Kerscher O

The Slx5/Slx8 heterodimer constitutes a SUMO-targeted Ubiquitin Ligase (STUbL) with an important role in SUMO-targeted degradation and SUMO-dependent signaling. This STUbL relies on SUMO-interacting motifs (SIMs) in Slx5 to aid in substrate targeting and carboxy-terminal RING domains in both Slx5 and Slx8 for substrate ubiquitylation. In budding yeast cells, Slx5 ...

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resides in the nucleus, forms distinct foci, and can associate with double-stranded DNA (dsDNA) breaks. However, it remains unclear how STUbLs interact with other proteins and their substrates. To further examine the targeting and functions of the Slx5/Slx8 STUbL we constructed and analyzed truncations of the Slx5 protein. Our structure-function analysis reveals a domain of Slx5 involved in nuclear localization and in the interaction with Slx5, SUMO, Slx8 and a novel interactor, the SUMO E3 ligase Siz1. We further analyzed the functional interaction of Slx5 and Siz1 in vitro and in vivo. We found that a recombinant Siz1 fragment is an in vitro ubiquitylation target of the Slx5/Slx8 STUbL. Furthermore, slx5 cells accumulate phosphorylated and sumoylated adducts of Siz1 in vivo. Specifically, we show that Siz1 can be ubiquitylated in vivo and is degraded in an Slx5-dependent manner when its nuclear egress is prevented in mitosis. In conclusion, our data provide a first look into the STUbL-mediated regulation of a SUMO E3 ligase.

Date: Nov. 06, 2013

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