Transcription and processing of mRNSs takes place in the nuclear interior,requiring that
hnRNPs move from transciption sites to NPCs at the nuclear periphery.Sites of transcription are also the sites of most mRNA processing 5' capping occurs as soon as the RNA is long enough for its 5' end ot emerge from a tunnel in the RNA polymerase holoenzyme;splicing begins during transcription, and 3' ends are generated by cleavage of the RNA while it is still a growing chain. When splicing or 3' processing is defective,mRNA are not exported.