Assembling pores

Despite the prominence of the nuclear pore structure, its assembly mechanism remains largely undescribed. On page 361, Madrid et al. show that one of the three transmembrane pore proteins is required for interphase assembly in yeast. The data suggest that insertion of nascent pores into the interphase nuclear envelope proceeds in a manner similar to that of postmitotic pore formation.

In budding yeast lacking Pom34 or Pom152, two of the transmembrane proteins, soluble pore components localized normally to the nuclear envelope. However, nuclear pore components were significantly mislocalized in cells depleted only for the third transmembrane protein, Ndc1. The Ndc1 defect was exaggerated in cells lacking Pom152.

Electron microscopy showed that double mutants had wide openings in the nuclear envelope, but little associated protein. These gaps allowed indiscriminant...