SIM-dependent enhancement of substrate-specific sumoylation by a ubiquitin ligase in vitro.

SUMO interaction motifs (SIMs), which mediate the non-covalent binding of the small ubiquitin-related modifier (SUMO) to other proteins, are usually involved in the recognition of sumoylated substrates by downstream effectors that transmit the biological signal of the modification. In budding yeast ubiquitin ligase Rad18, a SIM contributes to the recognition ...
of sumoylated PCNA as its physiological ubiquitylation target. We now show that Rad18 is also capable of enhancing PCNA sumoylation in a SIM-dependent manner in vitro, most likely by means of directing SUMO-loaded Ubc9 towards the substrate. The process shares important features with Rad18-dependent ubiquitylation, such as an exquisite specificity for the modification site on PCNA and the requirement of DNA, and the reaction proceeds under conditions that are widely used in other in vitro assays for SUMO ligase activity. Yet, there is no evidence that Rad18 contributes to PCNA sumoylation in vivo. Our findings therefore illustrate the problematic nature of in vitro sumoylation assays and highlight the danger of extrapolating from this type of experiment to the biological function of a SUMO-interacting protein.
Biochem. J.
Date: Nov. 14, 2013
Download Curated Data For This Publication
161741
Switch View:
  • Interactions 6