The genome of complex organisms is stashed away inside each cell's nucleus, a little like a sovereign shielded from the threatening world outside.
The genome cannot govern from its protective chamber, however, without knowing what's going on in the realm beyond and having the ability to project power there. Guarding access to the nuclear chamber is the job of large, intimidating gatekeepers known as nuclear pore complexes (NPCs), which stud the nuclear membrane, filtering all of the biochemical information passing in or out. In new research, scientists have for the first time glimpsed in three dimensions an entire subcomplex of the NPC; it's the key building block of this little-understood and evolutionarily ancient structure, an innovation fundamental to the development of nearly all multicellular life on Earth.
The findings, by Martin Kampmann, a graduate student in John D. Rockefeller Jr. Professor Günter Blobel's Laboratory of Cell Biology, add details to an unfolding picture of cellular evolution that shows a common architecture for the NPC and the vehicles that transport material between different parts of the cell, called coated vesicles. As early as 1980, Blobel proposed that internal membranes of cells - such as those encompassing the nucleus and vesicles - evolved from folds or invaginations of the outer cell membrane. Rockefeller scientists Brian T. Chait and Michael P. Rout suggested in a 2004 paper in PLoS Biology that both the NPC and vesicle coats, which contain similar protein folds, evolved from ancient membrane-coating proteins that stabilized these primordial internal membranes. "So far, it's been unclear how these ancient folds work in the nuclear pore complex," Kampmann says. "Now we can see that the α-solenoid folds form long, flexible arms and hinges that end in the more compact, globular β-propellers. The same architectural principle is found in clathrin, a common component of vesicle coats."