<Emphasis Type="Italic">Arabidopsis</Emphasis> cyclin-dependent kinase inhibitors are nuclear-localized and show different localization patterns within the nucleoplasm |
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Authors: | David A Bird Miruna M Buruiana Yongming Zhou Larry C Fowke Hong Wang |
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Institution: | (1) Department of Biology, University of Saskatchewan, Saskatoon, Canada, SK S7N 5E2;(2) Present address: Department of Botany, University of British Columbia, Vancouver, Canada, V6T 1Z4;(3) Present address: The National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, 4300070, China;(4) Department of Biochemistry, University of Saskatchewan, Saskatoon, Canada, S7N 5E5 |
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Abstract: | The Arabidopsis genome contains seven cyclin-dependent kinase (CDK) inhibitors (ICK for inhibitor/interactor with cyclin-dependent kinase)
which share a small conserved C-terminal domain responsible for the CDK-inhibition activity by these proteins. Different ICK/KRPs
have been shown to have unique expression patterns within tissues, organs and during the cell cycle. Previous studies have
shown that overexpressing one of the ICK/KRPs inhibits CDK activity, cell division, and profoundly affects plant growth and
development. In this study, we investigated the subcellular localization of the seven Arabidopsis ICK proteins and domains responsible for this localization. Using transgenic expression in Arabidopsis plants and transient expression in tobacco leaf cells, all ICK/KRPs fused to green fluorescent protein (GFP) were localized
to the nucleus, suggesting that the nucleus is the cellular compartment for the plant CDK inhibitors to function. While ICK2/KRP2,
ICK4/KRP6, and ICK5/KRP7 were localized to the nucleoplasm in a homogeneous manner, ICK1/KRP1, ICK3/KRP5, ICK6/KRP3, and ICK7/KRP4
showed a punctate pattern of localization. A small motif conserved amongst the latter group of ICK/KRPs is required to confer
this subcellular pattern as deletion of this motif from ICK7/KRP4 resulted in a shift from a punctate to a homogeneous pattern
of localization. While a single nuclear localization signal (NLS) is responsible for the nuclear localization of ICK2/KRP2,
multiple mechanisms for nuclear localization are suggested to exist for the other six ICK/KRPs since deletion mutants lacking
predicted NLS motifs and the conserved C-terminal domain are still localized in the nucleus. |
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Keywords: | Arabidopsis CDK inhibitor Cell cycle ICK KRP Nuclear localization |
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