No waiting at the nuclear pore complex

The group used single-molecule video microscopy, with a localization precision of about the width of a protein, to track single molecules of labeled, cargo-carrying receptors entering the NPC in vivo. They had previously used the same technique to look at the NPC in lifeless cells, but thought that the lack of vital activity—the absence of ion gradients in the cytoplasm, transcription in the nucleus—might affect the receptor's behavior. Instead, they found that the spatial and temporal details of NPC transport for the three receptors they studied was essentially the same: Once a receptor encountered the NPC, it was largely confined to a narrow central channel, and moved quickly through the pore to deliver its cargo. “There was no waiting at the gate,” says corresponding author David Grünwald.

The similarity between their in vivo data and their previous experiments suggests that nuclear import dynamics are determined mainly by cargo–receptor–pore interactions, and are mostly free of influence from other cell processes and other transported molecules, including, surprisingly, RNA. Grünwald suggests that perhaps RNA has its own export pathway through the NPC, a possibility the team intends to study in the future.