RNA export through the nuclear pore complex is directional

The changes occurring in mRNA organization during nucleo-cytoplasmic transport and export, are unknown. Moreover, directionality of mRNA passage through the nuclear pore complex (NPC) has not been examined within individual NPCs. We find that an mRNP is compact during nucleoplasmic travels compared to a more open structure after transcription and at the nuclear periphery. Compaction levels of nuclear transcripts could be modulated by varying levels of SR proteins and by changing genome organization. Nuclear mRNPs were mostly rod-shaped with distant 5`/3`-ends, although for some, the ends were in close proximity. The latter was more abundant in the cytoplasm and could be modified by translation inhibition. Exit from the NPC exhibited predominant 5’-first export for mRNAs and lncRNAs. In some cases, several adjacent NPCs were engaged in export of the same mRNA suggesting `gene gating`. Altogether, we show that the mRNP is a flexible structure during travels, with 5`-directionality during export.