Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents

This Article Full Text (PDF, 542K) Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Tuma, R. Search for Related Content PubMed Articles by Tuma, R. Related Collections Related Article Social Bookmarking                            What's this?

Transport if loaded

Nuclear transporters can be viewed as taxis that move cargo across the nuclear envelope. On page 649, Plafker et al. report that importin-11, a nuclear transport receptor, may be an especially selective cabbie. Importin-11 transports UbcM2, a ubiquitin (Ub)-conjugating enzyme, but it does so only when the enzyme is charged with a Ub at its active site.

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.

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.

Rabiya Tuma

rabiya{at}nasw.org

CiteULike    Complore    Connotea    Del.icio.us    Digg    Facebook    Reddit    Technorati    Twitter    What's this?

Related Article

Ubiquitin charging of human class III ubiquitin-conjugating enzymes triggers their nuclear import

Scott M. Plafker, Kendra S. Plafker, Allan M. Weissman, and Ian G. Macara
J. Cell Biol. 2004 167: 649-659. [Abstract] [Full Text] [PDF]

This Article Full Text (PDF, 542K) Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Tuma, R. Search for Related Content PubMed Articles by Tuma, R. Related Collections Related Article Social Bookmarking                            What's this?