Don't get stuck in the pore

Eukaryotic cells critically rely on a constant and intensive exchange of macromolecules between the cytoplasm and nucleoplasm across the barrier of the nuclear envelope. Nuclear pore complexes (NPCs) function as gates to mediate this transport, but why they grant the selective passage of transport receptor-cargo complexes and at the same time exclude most other cellular macromolecules is incompletely understood. In this issue of The EMBO Journal, Labokha et al (2013) extend our view on how certain NPC proteins form a sieve-like meshwork within the pore that is crucial for these functions.