Fragment ion mass spectra of AtTRS120 phosphopeptides found in AtTRS120:GFP IP-MS. Seedlings were grown in the light. (A) α-phosphosite of AtTRS120 at amino acid position S922. The spectrum with the phosphorylated S922 residue was identified with a 1% FDR, as can be seen in the deposited Skyline library. Note that the depicted y-ion series does not show the phosphorylation at S922. (B) β-phosphosite of AtTRS120 at amino acid position S971. (C) γ-phosphosite of AtTRS120 at amino acid position S1165. The y-ion series is highlighted in blue and non-annotated fragment ions in gray. Phosphorylated serines are written in bold letters. These sites are annotated as GSK3 sites in the PPSP (https://www.phosphosite.org) database. Note that not all phosphosites we detected in vivo (highlighted in yellow in Fig. 2 C) are depicted here. Spectra are taken from the deposited Skyline library, resulting from a MaxQuant search. At least three replicates were carried out for the IP-MS experiments. Related to Fig. 2.