Cells have devised many structures for transporting molecular cargo across their protective borders, but the nuclear pore complex, with its flower-like, eight-fold symmetry, stands out. Monstrously large by cellular standards, as well as versatile, this elaborate portal controls access to and exit from the headquarters of the cell, the nucleus. In research published June 4 in Cell, Rockefeller University scientists have uncovered crucial steps in the dynamic dance that dilates and constricts the nuclear pore complex -- the latest advance in their ongoing efforts to tease apart the mechanism by which its central channel admits specific molecules. Their work, based on quantitative biophysical data, has revealed that the nuclear pore complex is much more than the inert structure it was once thought to be.

"Prevailing wisdom cast the nuclear pore complex as a rigid conduit. Instead, we have found that it responds to the need for transport, opening and closing in an elegantly simple cycle," says study author Gunter Blobel, John D. Rockefeller Jr. Professor and head of the Laboratory of Cell Biology. "Our most recent study reveals how proteins called transport factors, known to chaperone legitimate cargo through the nuclear pore complex, prompt the ring at the middle of the central channel to dilate."

More than a billion years ago, certain cells gained an evolutionary advantage by surrounding their DNA in a protective membrane, creating the nucleus. However, this innovation created a problem: How to move molecules, in some cases very large ones, in and out. The nuclear pore complex was one solution, first described at Rockefeller over 50 years ago by Michael Watson, a postdoc in the Palade-Porter Laboratory. Years later, Blobel's lab identified the first of the proteins that act as the complex's building blocks: nucleoporins. For some time, it has been assumed that unstructured portions of some nucleoporin molecules guarded the complex's rigid central channel by creating a sort of gel-like barrier.