Abstract
SUMO1/Smt3, a ubiquitin-like protein modifier, is known to be conjugated to other proteins and modulate their functions in various important processes. Similar to the ubiquitin system, SUMO1/Smt3 is activated in an ATP-dependent reaction by thioester bond formation with E1 (activating enzyme), transferred to E2 (conjugating enzyme), and passed to a substrate lysine. It remained unknown, however, whether any SUMO1/Smt3 ligases (E3s) are involved in the final transfer of this modifier. Here we report a novel factor Siz1 (YDR409w) required for septin-sumoylation of budding yeast, possibly acting as E3. Siz1 is a member of a new family (Miz1, PIAS3, etc.) containing a conserved domain with a similarity to a zinc-binding RING-domain, often found in ubiquitin ligases. In the siz1 mutant septin-sumoylation was completely abolished. A conserved cysteine residue in the domain was essential for this conjugation. Furthermore, Siz1 was localized at the mother-bud neck in the M-phase and physically bound to both E2 and the target proteins.
MeSH terms
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Amino Acid Sequence
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Cell Cycle Proteins / genetics
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Cell Cycle Proteins / metabolism
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Electrophoretic Mobility Shift Assay
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Fluorescent Antibody Technique, Indirect
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Fungal Proteins / genetics
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Fungal Proteins / metabolism*
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Green Fluorescent Proteins
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Indoles
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Ligases / genetics
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Ligases / metabolism
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Luminescent Proteins / genetics
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Luminescent Proteins / metabolism
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Microscopy, Fluorescence
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Mitosis
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Molecular Sequence Data
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Phosphorylation
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Profilins
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Protein Binding
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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SUMO-1 Protein / genetics
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SUMO-1 Protein / metabolism*
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Saccharomyces cerevisiae / genetics
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Saccharomyces cerevisiae / metabolism
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Saccharomyces cerevisiae Proteins*
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Sequence Homology, Amino Acid
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Two-Hybrid System Techniques
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Ubiquitin-Conjugating Enzymes*
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Zinc Fingers / genetics
Substances
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CDC3 protein, S cerevisiae
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Cell Cycle Proteins
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Fungal Proteins
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Indoles
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Luminescent Proteins
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PCD1 protein, Pyrenopeziza brassicae
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Profilins
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Recombinant Fusion Proteins
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SUMO-1 Protein
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Saccharomyces cerevisiae Proteins
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Green Fluorescent Proteins
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DAPI
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Ubiquitin-Conjugating Enzymes
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Ligases
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ubiquitin-conjugating enzyme UBC9