| Qualifier | protein_id |
| Definition | protein identifier, issued by International collaborators. this qualifier consists of a stable ID portion (accessioned data before the end of 2018 uses a 3+5 format; from the end of 2018 new accessions may be extended to a 3+7 accession format with 3 position letters and 7 numbers) plus a version number after the decimal point. |
| Value Format | <identifier> |
| Example | /protein_id="AAA12345.1" /protein_id="AAA1234567.1" |
| Comment | when the protein sequence encoded by the CDS changes, only the version number of the /protein_id value is incremented; the stable part of the /protein_id remains unchanged and as a result will permanently be associated with a given protein; this qualifier is valid only on CDS features which translate into a valid protein. |