What are the sources of the Protein database sequences?
The protein sequences in the NCBI Protein database come from several different sources. There are GenPept translations for each of the coding sequences within the GenBank Nucleotide database. That means that there can be more than one protein sequence associated with a corresponding Nucleotide sequence record. example: DQ489526 There are records from other databases that are loaded periodically when builds become available such as UniProt (which has subsumed PIR and Swiss Prot records).
