SUMO-1: Ubiquitin gains weight

Abstract

The highly conserved polypeptide functions by covalently modifying other proteins. This modification has a well-established role in facilitating substrate degradation by the proteasome and can regulate some proteins by ways other than targeting then to the proteasome. It has now emerged that proteins bearing only distant similarity to ubiquitin can also be attached to specific proteins. The consequence of most of these modifications are not yet understood. However, two recent papers on one ubiquitin-like protein, SUMO-1, demonstrate a role in targeting a protein crucial for nucleocytoplasmic trafficking to the nuclear pore complex. These and other findings suggest a much wider influence of the 'ubiquitin system' on cell biology and raise intriguing regulatory and mechanistic questions.