Do sequences in IPI contain initiator methionines?
Each IPI entry contains the longest sequence described in a matching source database entry. Thus, if there are a choice of source database entries, one of whose sequences contains the methionine and one not, the sequence containing the methionine will be preferred. Of the source databases currently in use in IPI, UniProtKB/TrEMBL, Ensembl, and RefSeq sequences generally contain initiator methionines. UniProtKB/Swiss-Prot sequences also contain the initiator methionine, unless this methionine is believed not to be present in the mature protein (due to proteolytic cleavage). In this case, the methionine was not included in that sequence prior to UniProtKB release 9.5. After this release, UniProtKB/Swiss-Prot will be changing its representation of sequences to include the initiator methionione in all cases, similar to the other data sources.
