Model depicting partitioning of newly exported mRNAs between translation-engaged and stress granule-associated states in response to UPR activation. A working model depicting the functional states of newly exported mRNAs in homeostatic (active translation, low phospo-eIF2α) or stress-activated (reduced translation, elevated phospo-eIF2α) cellular states. This model highlights a role for translation-dependent RNA binding protein remodeling of newly exported mRNAs in determining mRNA recruitment into polyribosomes or SGs. As illustrated, under conditions of stress-induced translational inhibition, the nuclear RNA binding protein signature of newly exported mRNAs would be relatively long-lived and thus serve as a signal for ribonucleoprotein recruitment into stress granules, which could include both cytoplasmic and ER-associated forms. Once eIF2α phosphorylation is resolved, stress granule-associated mRNAs would resume translation, undergo RNA binding protein remodeling, and enter the polyribosome-associated pool. In this way, stress granules could serve as a triage station for newly exported mRNAs and undergo rapid mobilization following stress adaptation.
