Pro identifiers are URIs, globally unique identifiers.
Two forms of PURLs
The URIs have one of two forms:
where d is a digit.
In the second case, the identifiers denote the class of proteins that the UniProt accession is about. PRO uses these identifiers for the gene-organism level terms, and is considering using them for the isoform terms.
http://purl.obolibrary.org/obo/PR_Q10322 is the class of proteins sometimes known as *Probable E3 ubiquitin-protein ligase dma1* in Schizosaccharomyces. To be clear, this class of proteins includes any that is a gene product of the gene *dma1*, or of a population variant at the same locus, e.g. some mutation of *dma1*.
Response to access requests to PURLs
http://purl.obolibrary.org/obo/PR_.... represents a class defined in PRO, which isn't itself retrievable (protein classes can't be transmitted over wires) and so redirects (303) to
http://purl.obolibrary.org/obo/pr/about/PR_.... which then links to the descriptive page about that protein class provided by the PRO project.
In addition, we define PURLs to directly access RDF for a term, as an intermediate solution on the way to having the PRO server offer the same protocol as the Ontobee server. These PURLs will redirect to OntoBee formatted RDF/XML
http://purl.obolibrary.org/obo/pr.owl is the latest released version of the Protein Ontology in OWL 2 RDF/XML syntax. This is the reasoned-over version, one which has all the additional axioms that are inferred from the original edited ontology.