Nuclear retention is persistence of a molecule inside the cell nucleus through binding, assembly or restricted export. For example, an incompletely processed RNA can remain nuclear while a mature transcript is exported. Nuclear enrichment can arise through faster import, slower export or binding to a nuclear component, so a static image alone does not identify the underlying rate change. Nuclear retention is a localization mechanism distinct from synthesis occurring only in the nucleus. [ref]
Molecular Biology of the Cell, 4th edition by Bruce Alberts and others. Chapter 12, The Transport of Molecules between the Nucleus and the Cytosol
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