Elsevier

Experimental Cell Research

Volume 280, Issue 2, 1 November 2002, Pages 212-221
Experimental Cell Research

Regular Article
Ubc9 Is Essential for Viability of Higher Eukaryotic Cells

https://doi.org/10.1006/excr.2002.5634Get rights and content

Abstract

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 IκBα, 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.

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    1

    To whom correspondence and reprint requests should be addressed; Fax: (Japan 81)-22-217-6873. E-mail: [email protected].

    2

    Current address: PRESTO, Japan Science and Technology Corporation (JST), the Graduate University for Advanced Studies and National Institute of Genetics, Mishima 411–8540, Japan.

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