Hello all, I have a protein database for an organism downloaded from NCBI and almost all the proteins have prefix XP_. Does it mean that all the proteins with prefix XP_ are predicted and have no experimental evidence?
From this FAQ entry at NCBI.
Accession numbers that begin with the prefix XM_ (mRNA), XR_ (non-coding RNA), and XP_ (protein) are model RefSeqs produced either by NCBI’s genome annotation pipeline or copied from computationally annotated submissions to the INSDC. These RefSeq records are derived from the genome sequence and have varying levels of transcript or protein homology support. They represent the predicted transcripts and proteins annotated on the NCBI RefSeq contigs and may differ from INSDC mRNA submissions or from the subsequently curated RefSeq records (with NM_, NR_, or NP_ accession prefixes). These differences may reflect real sequence variation (polymorphism), or errors or gaps in the available genome sequence. The support for model RefSeq records should be further evaluated by comparing them to other sequence information available in Gene, Related Sequences, and BLAST reports.
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