mRNP

mRNP stands for messenger ribonucleoprotein particle, a dynamic complex that consists of a mature mRNA molecule bound by a constellation of RNA-binding proteins. This ribonucleoprotein assembly coordinates mRNA processing, protection, export from the nucleus, localization within the cell, and translation into protein. The composition and conformation of mRNPs change as the mRNA moves from transcription through cytoplasmic translation, enabling tight regulation of gene expression.

In the nucleus, nascent transcripts are associated with heterogeneous nuclear ribonucleoproteins and processing factors. The 5’ end cap is bound by the cap-binding complex, and splicing deposits the exon junction complex at exon boundaries. The mRNA is then cleaved, polyadenylated, and bound by poly(A) binding proteins. These nuclear mRNPs are tailored for processing and quality control, and they begin the export preparation in tandem with other export factors.

Export from the nucleus to the cytoplasm is mediated primarily by the nuclear export factor TAP/p15 and the mRNA bound mRNPs transit through the nuclear pore complex. Once in the cytoplasm, the mRNP composition shifts: the cap-binding complex is replaced by the cytoplasmic cap-binding protein eIF4E, translation initiation factors assemble, and poly(A) tails associate with PABP to promote translation. Additional remodeling factors and RNA helicases modify the mRNP to regulate localization, storage, or targeted decay.

mRNPs thus serve as functional units that influence mRNA stability, subcellular localization, translation efficiency, and turnover. Their proper regulation is essential for normal gene expression, and defects in mRNP assembly or remodeling are linked to various diseases.