This page lets you execute SPARQL queries against the Uniprot data stored in a RDF Gateway database. You can select from several example queries or enter your own. If you want to use your own SPARQL client here's the necessary information:
NOTE: this uses an early version of our SPARQL support package, so please let me know if something doesn't work that should. Also, I've initially set the query governor quite low, so complex queries might fail. Using LIMIT on complex queries might enable them to succeed where they would otherwise fail.