Meta-organization of Translation Centers Revealed by Proximity Mapping of Endoplasmic Reticulum Ribosome Interactors

We report a method to use BioID proximity labeling to map the sub-organization of translating mRNAs on the endoplasmic reticulum. This method first isolates membrane bound polysomes using a Sephacryl 400 resin-based enrichment followed by isolation of biotin labeled polysomes by streptavidin beads and high-throughput sequencing of the bound polysomes. We find that, for the two pools of polysomes labeled by either LRRC59 or Sec61beta BioID reporters, there is an interesting divergence in specific mRNAs that are entering into the secretory pathway such that secreted proteins are much more enriched towards the LRRC59 reporter with Sec61beta serving a more varied role in mRNA translation. Examination of mRNA from membrane bound polysomes labeled by BioID reporters of Sec61beta and LRRC59 compared to a null cell line as biological replicates.