Ubiquitylation of the 9-1-1 checkpoint clamp is independent of rad6-rad18 and DNA damage.
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.
Davies
Adelina A
AA
Cancer Research UK London Research Institute, Clare Hall Laboratories, Blanche Lane, South Mimms EN6 3LD, UK.
Neiss
Andrea
A
Ulrich
Helle D
HD
D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D016415:Sequence Alignment; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*; D054875:Ubiquitination
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C501395:RAD17 protein, S cerevisiae; C063607:RAD18 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C471606:RAD6 protein, S cerevisiae; D044763:Ubiquitin-Conjugating Enzymes; D046988:Proteasome Endopeptidase Complex