Open AccessRanBP2 associates with Ubc9p and a modified form of RanGAP1
Author(s) -
Hisato Saitoh,
Robert T. Pu,
Margaret M. Cavenagh,
Mary Dasso
Publication year - 1997
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.94.8.3736
Subject(s) - ran , xenopus , microbiology and biotechnology , nuclear transport , nuclear pore , small gtpase , gtpase , biology , cell nucleus , biochemistry , gene , cytoplasm , signal transduction
Ran is a small GTPase required for nuclear transport in eukaryotic cells [Gorlich, D. & Mattaj, I. W. (1996)Science 271, 1513–1518]. Mutants in Ran also show defects in mRNA processing, cell cycle regulation, and other aspects of nuclear function [Rush, M. G., Drivas, G. & D’Eustachio, P. (1996)BioEssays 18, 103–112; Sazer, S. (1996)Trends Cell Biol. 6, 81–85]. In an effort to understand the role of Ran in these diverse processes, we previously characterized 10 Ran interacting proteins (Rips) fromXenopus egg extracts. In this report, we present further characterization of a complex containing three of these Rips: p340RanBP2 , p88, and p18. We have cloned theXenopus homologue of RanGAP1, and we show here that p88 is a modified form of this protein. In RanGAP assays, the p340RanBP2 –p88–p18 complex contains GTPase-activating protein activity, indicating that RanGAP1 is not inactivated by modification. Rather, modification of RanGAP1 appears to be linked to its association with p340RanBP2 because we did not observe unmodified RanGAP1 in p340RanBP2 immunoprecipitates. We have also characterized p18, and we found that it is theXenopus homologue of Ubc9p, an E2 ubiquitin-conjugating enzyme that is required for cell cycle regulation [Seufert, W., Futcher, B. & Jentsch, S. (1995)Nature (London) 373, 78–81]. Using antibodies directed againstXenopus Ubc9p, we have confirmed that Ubc9p associates with p340RanBP2 inXenopus extracts. These results suggest Ubc9p’s role in cell cycle regulation may involve either modification of nuclear transport substrates or the nuclear transport machinery.