PRotein Ontology (PRO) Release 23.0 (29-Sep-2011)

There are 27624 PRO terms
    4 terms are in the 'organism-family' category.
   309 terms are in the 'family' category.
  18226 terms are in the 'gene' category.
  1387 terms are in the 'sequence' category.
  6052 terms are in the 'modification' category.
   100 terms are in the 'complex' category.
   466 terms are in the 'organism-gene' category.
   406 terms are in the 'organism-sequence' category.
   373 terms are in the 'organism-modification' category.
   178 terms are in the 'organism-complex' category.
   11 terms are in the 'union' category.
1574 terms have some kind of annotation, codifying the information from 1066 papers.
  2347 connections to GO (804 PRO terms).
   374 connections to MOD (327 PRO terms).
   604 connections to Pfam (361 PRO terms).
   338 connections to SO (317 PRO terms).
   306 annotations of a phenotype (299 PRO terms).

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

_Current changes_

1) To comply with the standard set by the Human Genome Nomenclature Committee, we replaced the word "antigen" with "molecule" for terms related to cell differentiation (CD). For example, CD9 antigen (PR:000005178) became CD9 molecule.
2) PRO terms at Category=gene received shorthand labels. These labels are meant to facilitate the ability to view the terms using software such as Cytoscape, where space is limited.
3) Synonyms have been sorted according to tag type (in the order EXACT, RELATED, BROAD, NARROW), followed by alphabetical order. 
4) PRO introduced inferred complexes. Inferred complexes are those that lack experimental evidence in an organism even though that organism is known to contain orthologs (or ortho-isoforms/ortho-modified forms) of every component of the complex found in another organism. Such complexes will be flagged with the evidence code ECO:0000088 ("Biological system reconstruction").

_Forthcoming changes_

1) Continue to add shorthand labels to terms.