Identifying The Genomic Origin of MS Detected Peptides and The Relating Alternative Splicing Event (A) The HIP-2 search result page of protein IPI00023636, displaying the evidence peptides detected in MS experiments. (B) The PEPPI sequence search result page of peptide 1, indicating the query peptide is produced from an exon-exon combination region. The corresponding PEPPI peptide can be mapped to 4 proteins. (C) The sequence search result page of peptide 2, indicating the peptide comes from an exon, and can be mapped to 5 proteins. (D) The search result of the wild-type MP2K7_HUMAN, showing the regions mapped by the peptides. Peptide 1 crosses the splice site of two exons (PEP000841690 and PEP000841692). Peptide 2 is produced from a single exon, PEP000841692. (E) The search result of the 3rd isoform of MP2K7_HUMAN, the protein that is mapped to the peptide 2 but not mapped to peptide 1. That is because the insertion of a cassette exon (PEP000841691) changed the sequence of the protein.