Imaging of single mRNA translation repression reveals diverse interactions with mRNP granules

During cellular stress mRNAs exit translation and accumulate in stress granules and P-bodies, although the dynamics of these interactions remain unclear. We imaged in real-time single mRNAs, their translational output, and mRNA-granule interactions during stress. We observed single mRNAs interacting with stress granules and P-bodies, with mRNAs moving bidirectionality between them. While translating mRNAs only interact with RNP granules dynamically, non-translating mRNAs can form stable associations that rigidly immobilize the mRNA within the granule. Imaging thousands of individual mRNA-granule interactions showed the probability of stable association increases with both mRNA length and granule size. Therefore, the recruitment of mRNAs to RNP granules involves both highly dynamic and stable interactions, influenced by several parameters, demonstrating a new layer of complexity in mRNA regulation during stress. One Sentence Summary mRNAs interact with stress granules and P-bodies in stable and dynamic manners influenced by ribosome association, mRNA length, and granule size.