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UbcM2 is an E2 enzyme, which works with E1 and E3 proteins to polyubiquitinate and tag proteins for degradation in the proteasome. To test whether importin-11 preferentially transports the Ub-charged UbcM2 or the unloaded enzyme, Plafker et al. performed coimmunoprecipitation assays with wild-type UbcM2, a mutant enzyme that is constitutively loaded with Ub, or a mutant that cannot be loaded. Importin-11 selectively bound the Ub-charged forms of UbcM2. Furthermore, in vitro pull-down assays showed that, if ATP or the E1 enzyme that loads Ub onto the UbcM2 active site were depleted, importin-11 did not bind UbcM2. In cell assays, catalytically inactive UbcM2 failed to localize to the nucleus.
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Only a subset of E2 enzymes bound to importin-11. This specific interaction may control the enzyme's access to potential substrates, including some involved in cell cycle progression. Plus, if importin-11 gobbles up all the Ub-charged UbcM2, then the enzyme cannot ubiquitinate cytoplasmic proteins.(Nuclear transporters can be viewed as ta) |
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发表于 2009-3-6 08:20
发表于 2015-5-29 13:26
