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Ubc9- and mms21-mediated sumoylation counteracts recombinogenic events at damaged replication forks

Dana Branzei1, Julie Sollier, Giordano Liberi

  • 1FIRC Institute of Molecular Oncology Foundation and Department of Biomedical Sciences and Biotechnology, Università degli Studi di Milano, Via Adamello 16, 20139 Milan, Italy. dana.branzei@ifom-ieo-campus.it

Cell
|November 4, 2006
PubMed

Insights

The Ubc9 and Mms21 enzymes prevent harmful cruciform structures during DNA replication. This sumoylation pathway works with Sgs1 to maintain genome stability, distinct from replication checkpoints.

Area of Science:

  • Molecular Biology
  • Genetics
  • DNA Repair

Background:

  • Ubc9 (SUMO-conjugating enzyme) and Siz1 (SUMO ligase) modify proteins like PCNA.
  • Sumoylated PCNA interacts with Srs2, a helicase that opposes recombination.
  • Replication stress response pathways are crucial for maintaining genome integrity.

Purpose of the Study:

  • To investigate the role of Ubc9 and Mms21 in DNA repair and replication.
  • To elucidate the mechanism by which sumoylation prevents aberrant DNA structures.
  • To understand the interplay between sumoylation, helicases, and genome stability.

Main Methods:

  • Genetic analysis of ubc9, mms21, siz1, srs2, pcna, sgs1, and top3 mutants.
  • Assessment of stalled-fork stability and cruciform structure accumulation.
  • Analysis of Rad51-dependent and sumoylation-dependent processes.

Main Results:

  • ubc9 mutants require checkpoint, recombination, and replication genes for growth.
  • ubc9 cells accumulate Rad51-dependent cruciform structures at damaged forks.
  • Ubc9 and Mms21 function with Sgs1 to resolve replication-associated X structures.

Conclusions:

  • Ubc9 and Mms21-mediated sumoylation is essential for resolving pathological cruciform structures at damaged forks.
  • This sumoylation pathway acts independently of canonical replication checkpoints.
  • The findings reveal a novel regulatory mechanism for maintaining genome stability during replication stress.

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