As the gateway to the nucleus, the nuclear pore complex manages hundreds of intricate cargo-handling operations every second. It decides which molecules enter the 120-nm long channel leading to the nucleus. The NPC ferries pairs of proteins as small as 50,000 daltons from cytoplasm to nucleus and shuttles ribosomal subunits as massive as 2 megadaltons going the opposite way.
To handle the array of molecular interactions on which these transactions depend, the NPC comprises 700 to as many as 1,000 polypeptides, known as nucleoporins or nups, drawn from about 30 different protein varieties. The locations and working relationships of those individual proteins have eluded researchers for more than two decades. But creative uses of cryoelectron tomography, X-ray crystallography, and computer modeling are taking biologists a collective step closer to the answer. Says Susan Wente, chair of cell and developmental biology at Vanderbilt University, "I think within two or three years ...
