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Cell. 2010 Jun 11;141(6):1080-7. doi: 10.1016/j.cell.2010.04.039.

Ubiquitylation of the 9-1-1 checkpoint clamp is independent of rad6-rad18 and DNA damage.

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  • 1Cancer Research UK London Research Institute, Clare Hall Laboratories, Blanche Lane, South Mimms EN6 3LD, UK.


A recent report proposed a function of the ubiquitin conjugation factors Rad6 and Rad18 comparable to the bacterial SOS response, controlling damage-induced transcriptional activation and contributing to checkpoint signaling. The relevant ubiquitylation target was identified as budding yeast Rad17, a subunit of the PCNA-like 9-1-1 checkpoint clamp. We report here that in fact all three subunits of the 9-1-1 complex are ubiquitylated. However, in contrast to previous results, we found modification of Rad17 to be independent of DNA damage, the Rad6-Rad18 complex, the putative acceptor site (lysine 197), and loading of the complex onto DNA. Consistently, we were unable to observe enhanced damage sensitivity or defects in checkpoint signaling in a rad17(K197R) mutant. Instead, our findings suggest that ubiquitylation of the 9-1-1 complex may be a background reaction that in some cases can mediate proteasomal degradation.

Copyright 2010 Elsevier Inc. All rights reserved.

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