mRNA accessibility within mRNPs as a determinant of gene expression.

mRNA accessibility within messenger ribonucleoproteins (mRNPs), in contrast to DNA accessibility within chromatin, has not yet been well established as an important determinant of gene expression. Recent work has revealed the importance of the exon junction complex (EJC) as an architectural protein complex that controls mRNP packaging. An important function of EJC-mediated mRNP packaging is to regulate m6A specificity. Structures of nuclear mRNP globules reveal an architecture in which EJCs reside within the inaccessible interior of globules. mRNA exon architecture may be a determinant of mRNA accessibility due to EJC-mediated mRNP packaging. Gene expression is a complex process requiring many control mechanisms to achieve a desired phenotype. DNA accessibility within chromatin is well established as an important determinant of gene expression. By contrast, while mRNA also associates with a complement of proteins, the exact nature of messenger ribonucleoprotein (mRNP) packaging and its functional relevance is not as clear. Recent reports indicate that exon junction complex (EJC)-mediated mRNP packaging renders exon junction-proximal regions inaccessible for m6A methylation, and that EJCs reside within the inaccessible interior of globular transcription and export (TREX) complex-associated nuclear mRNPs. We propose that 'mRNA accessibility' within mRNPs is an important determinant of gene expression that may modulate the specificity of a broad array of regulatory processes including but not limited to m6A methylation. [ABSTRACT FROM AUTHOR]