Polysome sorting controls mRNA localization and protein fate.

RNA localization and local translation are widespread phenomena that play key roles in a plethora of cellular processes ranging from embryo patterning to general cellular functions. The traditional paradigm assigns localization elements to cis-acting RNA sequences which assemble into complexes that regulate mRNA transport and translation, and the mRNA is generally transported while remaining translationally silent. However, recent evidence has shown that the nascent protein can also play an essential role in RNA localization and can enable polysomes to control their own transport and be delivered where and when they are needed. Two such examples are reviewed: translation factories and centrosomal mRNAs. Their comparison highlights the key role of cotranslational interactions in the spatiotemporal control of protein synthesis and protein fate.