Single-Molecule Quantification of Translation-Dependent Association of mRNAs with the Endoplasmic Reticulum

It is well established that mRNAs encoding secretory or membrane-bound proteins are translated on the surface of the endoplasmic reticulum (ER). The extent to which mRNAs that encode cytosolic proteins associate with the ER, however, remains controversial. To address this question, we quantified the number of cytosolic protein-encoding mRNAs that co-localize with the ER using single-molecule RNA imaging in fixed and living cells. We found that a small but significant number of mRNAs that encode cytosolic proteins associate with the ER and show that this interaction is translation dependent. Furthermore, we demonstrate that cytosolic protein-encoding transcripts can remain on the ER with dwell times consistent with multiple rounds of translation and have higher ribosome occupancies than transcripts translated in the cytosol. These results advance our understanding of the diversity and dynamics of localized translation on the ER. [Display omitted] •A small fraction of mRNAs encoding cytosolic proteins co-localize with the ER•ER association of mRNAs is translation dependent•Cytosolic or ER localization of a transcript affects its translation The cytoplasmic location of a transcript can influence gene expression. Voigt et al. have quantified the co-localization of mRNAs with the ER with single-molecule resolution in fixed and living cells. Transcripts that associate with the ER can have higher ribosome occupancies.