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

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

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cell Cycle Proteins / metabolism*
  • DNA Damage*
  • DNA-Binding Proteins / metabolism*
  • Humans
  • Molecular Sequence Data
  • Nuclear Proteins / metabolism*
  • Proteasome Endopeptidase Complex / metabolism
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Sequence Alignment
  • Ubiquitin-Conjugating Enzymes / metabolism*
  • Ubiquitination

Substances

  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Nuclear Proteins
  • RAD17 protein, S cerevisiae
  • RAD18 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • RAD6 protein, S cerevisiae
  • Ubiquitin-Conjugating Enzymes
  • Proteasome Endopeptidase Complex