The ubiquitin-like proteins SMT3 and SUMO-1 are conjugated by the UBC9 E2 enzyme

The ubiquitin-like proteins SMT3 and SUMO-1 are conjugated by the UBC9 E2 enzyme

^*Deutsches Krebsforschungszentrum, Angewandte Tumorvirologie, Im Neuenheimer Feld 242, D-69120 Heidelberg, Germany; and ^‡Zentrum für Molekulare Biologie der Universität Heidelberg, Im Neuenheimer Feld 282, D-69120 Heidelberg, Germany

Edited by Alexander Varshavsky, California Institute of Technology, Pasadena, CA, and approved November 21, 1997 (received for review October 15, 1997)

Abstract

The ubiquitin-like protein SMT3 from Saccharomyces cerevisiae and SUMO-1, its mammalian homolog, can be covalently attached to other proteins posttranslationally. Conjugation of ubiquitin requires the activities of ubiquitin-activating (E1) and -conjugating (E2) enzymes and proceeds via thioester-linked enzyme-ubiquitin intermediates. Herein we show that UBC9, one of the 13 different E2 enzymes from yeast, is required for SMT3 conjugation in vivo. Moreover, recombinant yeast and mammalian UBC9 enzymes were found to form thioester complexes with SMT3 and SUMO-1, respectively. This suggests that UBC9 functions as an E2 in a SMT3/SUMO-1 conjugation pathway analogous to ubiquitin-conjugating enzymes. The role of yeast UBC9 in cell cycle progression may thus be mediated through its SMT3 conjugation activity.

Footnotes

↵ † S.E.S., K.M., and D.L. contributed equally to this paper.
↵ § M.S. and S.J. share senior authorship.
↵ ¶ To whom reprint requests should be addressed. e-mail: Jentsch{at}sun0.urz.uni-heidelberg.de.
This paper was submitted directly (Track II) to the Proceedings Office.
Abbreviations: HA, influenza virus hemagglutinin epitope; WT, wild type.