mRNA Export-An Integrative Component of Gene Expression
Susanne Röther and Katja Sträßer
MRNA export is an indispensable step during the complex process of eukaryotic gene expression: the mRNA, created by RNA polymerase II in the nucleus, has to be transported to the cytoplasm, where the ribosomes are responsible for the synthesis of the encoded protein. This transport process is not restricted to the simple passage of the mRNA through the nuclear pore complex, which spans the nuclear envelope, but is embedded into the gene expression pathway. During transcription, the message is capped, spliced and polyadenylated and mRNA export factors are loaded onto the nascent transcript. This maturation and assembly of the mRNA into a mature messenger ribonucleoprotein particle is controlled by nuclear surveillance systems: the nuclear exosome and the Mlp1‑2 system prevent the escape of aberrant transcripts to the cytoplasm. Only correctly assembled mRNPs are transported through the nuclear pore to the cytoplasm by the mRNA export receptor Mex67‑Mtr2/Tap‑p15, which is recruited to the mRNA by interaction with the mRNP‑bound TREX complex and SR proteins. This tight coupling between the single steps of the nuclear gene expression guarantees an efficient and accurate transfer of the genetic information to the cytoplasm.