title: The Arabidopsis cullin AtCUL1 is modified by the ubiquitin-related protein RUB1.
abstract: The ubiquitin-like protein RUB1 is conjugated to target proteins by a mechanism similar to that of ubiquitin conjugation. Genetic studies in Arabidopsis thaliana have implicated the RUB-conjugation pathway in auxin response. The first step in the pathway is RUB activation by a bipartite enzyme composed of the AXR1 and ECR1 proteins. Ubiquitin activation is an ATP-dependent process that involves the formation of an AMP-ubiquitin intermediate. Here we show that RUB activation by AXR1-ECR1 also involves formation of an AMP-RUB intermediate and that this reaction is catalyzed by the ECR1 subunit alone. In addition, we identified an Arabidopsis protein called RCE1 that is a likely RUB-conjugating enzyme. RCE1 works together with AXR1-ECR1 to promote formation of a stable RUB conjugate with the Arabidopsis cullin AtCUL1 in vitro. Using a tagged version of RUB1, we show that this modification occurs in vivo. Because AtCUL1 is a component of the ubiquitin protein ligase SCF(TIR1), a complex that also functions in auxin response, we propose that RUB modification of AtCUL1 is important for auxin response.
authors.affiliation: Institute for Cellular and Molecular Biology, Section of Molecular, Biology, University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: del Pozo
authors.forename: M
authors.initials: M
authors.lastname: Estelle
mesh_terms: D000249:Adenosine Monophosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D017360:Arabidopsis; D029681:Arabidopsis Proteins; D017124:Conserved Sequence; D004952:Esters; D006133:Growth Substances; D008025:Ligases / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D017386:Sequence Homology, Amino Acid; D013438:Sulfhydryl Compounds; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*
chemical_list: C081977:AXR1 protein, Arabidopsis; D029681:Arabidopsis Proteins; C112755:ECR1 protein, Arabidopsis; D004952:Esters; D006133:Growth Substances; D010940:Plant Proteins; C513170:RUB1 protein, Arabidopsis; D013438:Sulfhydryl Compounds; D014452:Ubiquitins; D000249:Adenosine Monophosphate; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D008025:Ligases