Fig. 2

Frameshift-isoforms are translated and are enriched in PxxP motifs. a Number of unique peptides identified in mouse brain lysate mapping to predicted frameshift C-termini (unambiguously identified frameshift C-termini marked in red); some peptides map to the same frameshift sequences. b Schematic representation of targeted SIM MS method. Peptide mass peaks with the highest relative intensities (red circles) are chosen for MS2 fragmentation and subsequent identification. By focusing on only a narrow mass range, specific peptide mass peaks can be targeted and, due to decreased background, fragmented and further identified. c Targeting of peptide NLAADPDLAQVLEMLK, a proteotypic peptide mapping to the novel frameshift C-terminus of SGSH, and SGQASPSRPESPRPPFDL, a peptide mapping to the predicted frameshift isoform of DNM1, which has been annotated as isoform 4, using targeted SIM MS. d Frequency of SH3-domain-binding proline-rich motifs in mouse full-length C-termini (black) and frameshift C-termini fulfilling the criteria defined in Fig. 1a (red)