EXPLORING NATIVE NUCLEAR-PORE COMPLEX STRUCTURE AND CONFORMATION BY SCANNING FORCE MICROSCOPY IN PHYSIOLOGICAL BUFFERS

We have used the scanning force microscope to image the cytoplasmic an d nuclear faces of the nuclear pore complex (NPC) in physiological buf fer environment. In agreement with previous electron micrographs recor ded from dehydrated specimens, we have been able to reproducibly disti nguish a high degree of asymmetry between the nuclear and cytoplasmic surfaces of the nuclear pore complex. Very much like seen in the elect ron microscope, the cytoplasmic face of the nuclear pore complex appea rs ''donutlike'' with a massive, approximately 18 nm high annulus surr ounding the membrane pore. In contrast, the nuclear face of the pore c omplex looks like a approximately 36 nm high ''dome'' in the scanning force microscope, which in the electron microscope is resolved into a tenuous ring from which eight thin filaments emanate that are joined d istally by a terminal ring, thus forming a ''basket'' or ''fishtrap.'' In addition, we were able to visualize distinct structural changes oc curring upon mechanical manipulation of the nuclear pore complex perip hery with the scanning tip. These preliminary data provide us with the intriguing future possibility to directly correlate NPC structure wit h function.