HA-affinity purification samples were briefly separated by 10% SDS-PAGE and excised into a low molecular weight (<55 kDa) and a high molecular weight (>55 kDa) gel slice. Tryptic digest and peptide elution were described before (34 (link)). Samples were treated as described in Supplemental Methods and were directly injected into a Q Exactive HF spectrometer (Thermo Scientific). A 90 min gradient of 2–95% buffer B (80% acetonitrile, 0.5% formic acid) at a constant flow rate was used to elute peptides. Mass spectra were acquired in a data-dependent fashion using a top15 method for peptide sequencing. Raw data was processed with MaxQuant Version 1.6.3.3 using default parameters (35 (link)). MS/MS spectra were searched against a Chlamydonomas database (https://phytozome.jgi.doe.gov/pz/portal.html) concatenated with reverse copies of all sequences and a list of amino acid sequences of frequently observed contaminants (minimal peptide length = 7, minimal peptide = 1 (razor or unique), PSM FDR = 0.01). Label-free quantification (minimal ratio count = 2) and ‘match between runs’ (matching time window = 0.7 min, alignment time window = 20 min) was enabled (35 (link)). All raw files, MaxQuant results and parameter files are available at ProteomeXchange (see Data Availability).