1. Max Planck Institute for Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany, Center for Biological Sequence Analysis, Technical University of Denmark, 2800 Lyngby, Denmark, Micalis, AgroParisTech-INRA, Domaine de Vilvert, 78352 Jouy-en-Josas, France, and Proteome Center Tuebingen, Auf der Morgenstelle 15, 72076 Tübingen, Germany