Figure 1.

(A) An mRNP is fully configured in the nucleus cotranscriptionally. It exits the nucleus equipped with proteins that define its localization, translation, and decay patterns. After each completed step, individual regulatory proteins are shed away in a step-by-step fashion. (B) An mRNP structure changes dynamically throughout the lifetime of an mRNA in the cytoplasm through the diffusion-driven association and disassociation process. Transcriptional events in the nucleus are separated physically and temporally from those that occur in the cytoplasm, and have little effect on the formation of a functional mRNP.