The ubiquitin conjugation system is involved in the disassembly of cilia/flagella
Kaiyao Huang, Dennis R. Diener, and Joel L. Rosenbaum
Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520
The disassembly of cilia/flagella is linked to the cell cycle and environmental cues. We have found that ubiquitination of flagellar proteins is an integral part of flagellar disassembly. Free ubiquitin and the ubiquitin-conjugating enzyme CrUbc13 were detected in flagella and several proteins were ubiquitinated in isolated flagella when exogenous ubiquitin and ATP were added. These data suggest that the ubiquitin conjugation system operates in flagella. Ubiquitinated flagellar proteins increased during flagellar resorption and increased more dramatically during flagellar resorption in intraflagellar transport (IFT) mutants, suggesting that disassembly products are labeled with ubiquitin and transported to the cell body by IFT. Substrates of the ubiquitin conjugation system include α-tubulin (but not β-tubulin) and two signaling proteins involved in the mating process, cGMP-dependent kinase and the cation channel PKD2 (polycystic kidney disease 2). Ubiquitination of flagellar proteins was enhanced early in mating, suggesting that ubiquitination also plays an active role in regulating signaling pathways in flagella.
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