Ubc9 is essential for viability of higher eukaryotic cells

Exp Cell Res. 2002 Nov 1;280(2):212-21. doi: 10.1006/excr.2002.5634.


Ubc9 is an enzyme involved in the conjugation of SUMO-1 (small ubiquitin related modifier 1) to target proteins. The SUMO-1 conjugation system is well conserved from yeasts to higher eukaryotes, but many SUMO-1 target proteins reported recently in higher eukaryotic cells, including IkappaBalpha, MDM2, p53, and PML, are not present in yeasts. To determine the physiological roles of SUMO-1 conjugation in higher eukaryotic cells, we constructed a conditional UBC9 mutant of chicken DT40 cells containing the UBC9 transgene under control of a tetracycline-repressible promoter and characterized their loss of function phenotypes. Ubc9 disappeared 3 days after the addition of tetracycline and the increase in viable cell number stopped 4 days after the addition of drug. In contrast to the cases of ubc9 mutants of budding and fission yeasts, which show defects in progression of G2 or early M phase and in chromosome segregation, respectively, we did not observe accumulation of cells in G2/M phase or a considerable increase in the frequency of chromosome missegregation upon depletion of Ubc9 but we did observe an increase in the number of cells containing multiple nuclei, indicating defects in cytokinesis. A considerable portion of the Ubc9-depleted cell population was committed to apoptosis without accumulating in a specific phase of the cell cycle, suggesting that chromosome damages are accumulated in Ubc9-depleted cells, and apoptosis is triggered without activating checkpoint mechanisms under conditions of SUMO-1 conjugation system impairment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Bacterial Agents / metabolism
  • Apoptosis / physiology
  • Cell Cycle / physiology
  • Cell Line
  • Cell Nucleus / genetics
  • Cell Nucleus / metabolism*
  • Cell Survival / physiology*
  • Chickens
  • Chromosome Segregation
  • Flow Cytometry
  • In Situ Hybridization, Fluorescence
  • Ligases / genetics*
  • Ligases / metabolism*
  • Phenotype
  • Promoter Regions, Genetic
  • SUMO-1 Protein / genetics
  • SUMO-1 Protein / metabolism*
  • Tetracycline / metabolism
  • Transgenes
  • Ubiquitin-Conjugating Enzymes*


  • Anti-Bacterial Agents
  • SUMO-1 Protein
  • Ubiquitin-Conjugating Enzymes
  • Ligases
  • ubiquitin-conjugating enzyme UBC9
  • Tetracycline