PRotein Ontology (PRO) Release 73.0 (01-Jul-2026)

There are 236541 active PRO terms in the Protein Ontology. Those representing individual proteins are mapped to 169481 UniProtKB sequences.
      17 terms are in the 'organism-polymer' category.
      13 terms are in the 'polymer' category.
     525 terms are in the 'family' category.
   23967 terms are in the 'gene' category.
      29 terms are in the 'seqgroup' category.
    8067 terms are in the 'sequence' category.
    4968 terms are in the 'modification' category.
     233 terms are in the 'complex' category.
      43 terms are in the 'organism-family' category.
   88802 terms are in the 'organism-gene' category.
     202 terms are in the 'organism-seqgroup' category.
   69098 terms are in the 'organism-sequence' category.
   39917 terms are in the 'organism-modification' category.
     505 terms are in the 'organism-complex' category.
      21 terms are in the 'union' category.
      84 terms are in the 'external' category.
2262 terms have some kind of annotation, codifying the information from 1643 papers.
    4414 connections to GO (1718 PRO terms).
      27 connections to SO (24 PRO terms).
     610 annotations of a phenotype (585 PRO terms).

The ontology includes a subset of terms from other ontologies and resources that are used for logical definitions.

_Current changes_

As previously announced, PRO will reduce in size by obsoleting many 'organism-gene' terms that: (1) are automatically processed based on UniProtKB as data source; (2)
 have not had any value-added information over and above what UniProt provides; and (3) represent proteins from organisms for which PRO has not seen much adoption.
 All such terms have direct mappings to UniProtKB and, accordingly, most users opt to use UniProtKB directly. Term deprecation will proceed organism-by-organism.

The first wave of deprecations goes into effect with this release and will be for proteins from:
 Dictyostelium discoideum (slime mold; NCBITaxon:44689; 3813 terms)
 Danio rerio (zebrafish; NCBITaxon:7955; 3437 terms)
 Drosophila melanogaster (fruit fly; NCBITaxon:7227; 5564 terms)
 Caenorhabditis elegans (worm; NCBITaxon:6239; 6879 terms).

Terms fitting the above criteria will be moved to a separate 'obsolete terms' file that will NOT be imported into PRO. Instead, the terms will be available for download as OBO-format stanzas in the file 'pro_deprecated.obo'.

Terms that have been obsoleted that do NOT fit the above criteria will still be distributed with PRO. Any term obsoleted for any reason can be reactivated by request using the PRO issue tracker at http://purl.obolibrary.org/obo/pr/tracker.

_Forthcoming changes_

The second wave of deprecations will occur with release 74.0 and will include proteins from:
Arabidopsis thaliana (mouse-ear cress), Saccharomyces cerevisiae S288C (baker's yeast), and Rattus norvegicus (rat).