Protein Information Resource, Georgetown University Medical Center, Washington, DC 20007, USA, Department of Computer Engineering, Muxc4x9fla Sxc4xb1tkxc4xb1 Koxc3xa7man University, Muxc4x9fla 48000, Turkey, Center for Bioinformatics and Computational Biology and Protein Information Resource, University of Delaware, Newark, DE 19711, USA, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SD, UK and Swiss Institute of Bioinformatics, Centre Medical Universitaire, 1 rue Michel Servet, 1211 Geneva 4, Switzerland.