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Plant Physiology Preview Published on June 9, 2006; 10.1104/pp.106.081406
Received April 7, 2006 Analysis of the subcellular localization, function and proteolytic control of the Arabidopsis CDK inhibitor ICK1/KRP1
University group at the Max-Planck-Institute for Plant Breeding, Max-Delbrück-Laboratorium, Department of Botany III, University of Cologne, Carl von Linné Weg 10, 50829 Köln, Germany * Corresponding author; email: schnitt{at}mpiz-koeln.mpg.de.
Recent studies have shown that CDK inhibitors can have a tremendous impact on cell cycle progression in plants. In animals, CDK inhibitors are tightly regulated, especially by posttranslational mechanisms of which control of nuclear access and regulation of protein turnover are particularly important. Here we address the posttranslational regulation of ICK1/KRP1, an Arabidopsis CDK inhibitor. We show that ICK1/KRP1 exerts its function in the nucleus and its presence in the nucleus is controlled by multiple nuclear localization signals as well as by nuclear export. In addition, we show that ICK1/KRP1 localizes to different subnuclear domains, i.e. in the nucleoplasm and to the chromocenters, hinting at specific actions within the nuclear compartment. Localization to the chromocenters is mediated by an N-terminal domain, in addition we find that this domain may be involved in cyclin binding. Further we demonstrate that ICK1/KRP1 is an unstable protein and degraded by the 26S proteasome in the nucleus. This degradation is mediated by at least two domains indicating the presence of at least two different pathways impinging on ICK1/KRP1 protein stability.
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