This subsection of the ‘Names and taxonomy’ section shows the unique identifier assigned by the NCBI to the source organism of the protein. This is known as the ‘taxonomic identifier’ or ‘taxid’.
A ‘taxonomic identifier’ consists of one to seven digits.
The NCBI provides unique taxonomic identifiers for all organisms (taxons) that are represented in the international nucleotide sequence database and in UniProtKB. In the case of an organism that is solely represented in UniProtKB the relevant ‘taxonomic identifier’ may not be visible from the NCBI taxonomic database but is stored in the UniProt taxonomic database.
Taxonomic identifiers are generally stable, but under some rare circumstances, they may change, for instance when one taxon is merged with another.
We also provide a link to the NCBI taxonomy database.