Proxiome at the 40S ribosomal head region according to proximity labeling MS experiments

The in vivo labeling technique Biotin identification (BioID, Roux et al., 2012) was used to capture proteins in the microenvironments of the ribosomal proteins Rps3 (uS3) and Rps20 (us10) in Saccharomyces cerevisiae. Biotinylated proteins were captured from cell lysates using affinity purification and subjected to SDS-PAGE followed by in-gel digestion with trypsin. Liquid chromatography-mass spectrometry (LC-MS) was performed to identify and relatively quantify peptides and thus proteins. Relative quantification of proteins was based on stable isotope labeling with amino acids in cell culture (SILAC). To account for putative differences in the expression levels of the enriched proteins, an input control was analyzed as well. To this end, an aliquot of the cell lysate was taken prior to protein enrichment and analyzed as well. Beyond the known and expected interaction partners of Rps3 and Rps20, we identified proteins not known to co-localize with them. Moreover, we could also observe changes in their environment when the WD40-repeat protein Asc1/RACK1 was absent from the head region.