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. © 2010 Elsevier Inc.
Davies, A. A., Neiss, A., & Ulrich, H. D. (2010). Ubiquitylation of the 9-1-1 checkpoint clamp is independent of Rad6-Rad18 and DNA damage. Cell, 141(6), 1080–1087. https://doi.org/10.1016/j.cell.2010.04.039