Spoke ring and anchorage of nuclear pore complex revealed by high resolution transmission electron microscopy

Using several different methods, the nuclear pore complex (NPC) was shown to be anchored in the nuclear envelope into the specific curved region, called pore membrane. Three transmembrane nucleoporins in the equatorial region of NPC contain hydrophobic stretches, which exhibit the ability to intersect the phospholipid bilayer. Using transmission electron microscopy, we observed three different evaluable morphological situations in the section through the NPC spoke ring (SR). We suppose that some sections are directed through one type of subunit that is responsible for anchoring. Other sections are directed through the second type of subunit that may provide pore membrane bending. Finally, the spoke ring is sectioned between aforementioned subunits where the pore membrane is best preserved. The proposed anchor is represented by the chains of protein complexes which replace phospholipid bilayer in a relatively large area. Second subunit, presumed bending module is represented by the bundles of chains copying the shape of the pore membrane from the side of the NPC. This work is based on very high resolution resulting in unique and complicated images of tangled and cut off protein chains, nevertheless, it provides insight into how some proteins interact with or replace the membrane.