1/17/2024 0 Comments Disassembly free![]() Finally, Ubp14 and human isopeptidase T are shown to be functional homologs by complementation analysis. Surprisingly, overproduction of wild-type Ubp14 can inhibit degradation of some proteins as well. Inhibition of degradation is also seen when an active site mutant of Ubp14 is overproduced in vivo. Increasing the steady-state levels of ubiquitin chains in wild-type cells (by expressing a derivative of ubiquitin with an altered C-terminus) inhibits protein degradation to a degree comparable with that observed in ubp14delta cells. Correspondingly, deletion of the UBP14 gene from yeast cells results in a striking accumulation of free ubiquitin chains, which correlates with defects in ubiquitin-dependent proteolysis. We describe a yeast deubiquitinating enzyme, Ubp14, that specifically disassembles unanchored ('free') ubiquitin chains in vitro, a specificity shared by mammalian isopeptidase T. Degradation of many eukaryotic proteins requires their prior ligation to polyubiquitin chains, which target substrates to the 26S proteasome, an abundant cellular protease.
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