Regulated mRNA Transport

The transport of mRNAs from the nucleus to specific locations in the cytoplasm is a highly regulated process aided by a variety of cis- and trans-acting elements.

mRNA contains cis-acting elements at the 3’ and, less often, at the 5’ untranslated regions of the mRNA. These localization elements, also known as zip-code regions, can be up to a thousand base pairs in length and determine the cytoplasmic localization of the exported mRNA.

The trans-acting elements include mRNA binding proteins that recognize specific sequences or structures formed by the mRNA and, together with RNA, form heterogeneous nuclear ribonucleoprotein particles.  

mRNA in these particles is then exported through nuclear pore complexes with the help of exporter proteins that associate with both the mRNA and the nuclear pore complexes. 

Nucleus-specific proteins detach from the mRNA before it is exported to the cytoplasm while exporter proteins leave the mRNA in the cytoplasm and return to the nucleus for further mRNA export.

Some mRNAs are transported to a specific location as directed by their zip-code sequences before starting protein production and remain translationally inactive until they reach their targe