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Genetics, Vol. 179, 177-192, May 2008, Copyright © 2008
doi:10.1534/genetics.108.089128

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The Small Ubiquitin-Like Modifier (SUMO) and SUMO-Conjugating System of Chlamydomonas reinhardtii

Ying Wang1, Istvan Ladunga2, Amy R. Miller, Kempton M. Horken, Thomas Plucinak, Donald P. Weeks and Cheryl P. Bailey3

Department of Biochemistry and Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588-0664

3 Corresponding author: Department of Biochemistry, N106 Beadle Center, 1901 Vine St., University of Nebraska, Lincoln, NE 68588-0664.
E-mail: cbailey7{at}unl.edu

The availability of the complete DNA sequence of the Chlamydomonas reinhardtii genome and advanced computational biology tools has allowed elucidation and study of the small ubiquitin-like modifier (SUMO) system in this unicellular photosynthetic alga and model eukaryotic cell system. SUMO is a member of a ubiquitin-like protein superfamily that is covalently attached to target proteins as a post-translational modification to alter the localization, stability, and/or function of the target protein in response to changes in the cellular environment. Three SUMO homologs (CrSUMO96, CrSUMO97, and CrSUMO148) and three novel SUMO-related proteins (CrSUMO-like89A, CrSUMO-like89B, and CrSUMO-like90) were found by diverse gene predictions, hidden Markov models, and database search tools inferring from Homo sapiens, Saccharomyces cerevisiae, and Arabidopsis thaliana SUMOs. Among them, CrSUMO96, which can be recognized by the A. thaliana anti-SUMO1 antibody, was studied in detail. Free CrSUMO96 was purified by immunoprecipitation and identified by mass spectrometry analysis. A SUMO-conjugating enzyme (SCE) (E2, Ubc9) in C. reinhardtii was shown to be functional in an Escherichia coli-based in vivo chimeric SUMOylation system. Antibodies to CrSUMO96 recognized free and conjugated forms of CrSUMO96 in Western blot analysis of whole-cell extracts and nuclear localized SUMOylated proteins with in situ immunofluorescence. Western blot analysis showed a marked increase in SUMO conjugated proteins when the cells were subjected to environmental stresses, such as heat shock and osmotic stress. Related analyses revealed multiple potential ubiquitin genes along with two Rub1 genes and one Ufm1 gene in the C. reinhardtii genome.







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