PRotein Ontology (PRO) Release 2.1 Note 24-September-2008 The Protein Ontology Consortium--Georgetown University Medical Center (GUMC), The Jackson Laboratory, and the Department of Philosophy, State University of New York at Buffalo--is pleased to announce PRO Release 2.1 (24-September-2008). PRO describes the relationships of proteins and protein evolutionary classes, delineates the multiple protein forms of a gene locus (ontology for protein forms), and interconnects existing ontologies. Further information is available at http://pir.georgetown.edu/pro/. PRO Release 2.1 consists of 1051 terms with their respective definitions, comprising 153 proteins.