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A short motif in Arabidopsis CDK inhibitor ICK 1 decreases the protein level, probably through a ubiquitin‐independent mechanism
Author(s) -
Li Qin,
Shi Xianzong,
Ye Shengjian,
Wang Sheng,
Chan Ron,
Harkness Troy,
Wang Hong
Publication year - 2016
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.13223
Subject(s) - f box protein , ubiquitin , biology , mutant , arabidopsis , yeast , microbiology and biotechnology , cyclin dependent kinase , proteasome , biochemistry , ubiquitin ligase , protein degradation , cell cycle , gene
Summary The ICK / KRP family of cyclin‐dependent kinase ( CDK ) inhibitors modulates the activity of plant CDK s through protein binding. Previous work has shown that changing the levels of ICK / KRP proteins by overexpression or downregulation affects cell proliferation and plant growth, and also that the ubiquitin proteasome system is involved in degradation of ICK / KRP s. We show in this study that the region encompassing amino acids 21 to 40 is critical for ICK 1 levels in both Arabidopsis and yeast. To determine how degradation of ICK 1 is controlled, we analyzed the accumulation of hemagglutinin ( HA ) epitope‐tagged ICK 1 proteins in yeast mutants defective for two ubiquitin E3 ligases. The highest level of HA ‐ ICK 1 protein was observed when both the N‐terminal 1–40 sequence was removed and the SCF ( SKP 1–Cullin1–F‐box complex) function disrupted, suggesting the involvement of both SCF ‐dependent and SCF ‐independent mechanisms in the degradation of ICK 1 in yeast. A short motif consisting of residues 21–30 is sufficient to render green fluorescent protein ( GFP ) unstable in plants and had a similar effect in plants regardless of whether it was fused to the N‐terminus or C‐terminus of GFP . Furthermore, results from a yeast ubiquitin receptor mutant rpn10Δ indicate that protein ubiquitination is not critical in the degradation of GFP ‐ ICK 1 1–40 in yeast. These results thus identify a protein‐destabilizing sequence motif that does not contain a typical ubiquitination residue, suggesting that it probably functions through an SCF ‐independent mechanism.

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