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 and nuclear faces of the nuclear pore complex (NPC) in physiological buffer environment. In agreement with previous electron micrographs recorded from dehydrated specimens, we have been able to reproducibly distinguish a high degree of asymmetry between the nuclear and cytoplasmic surfaces of the nuclear pore complex. Very much like seen in the electron microscope, the cytoplasmic face of the nuclear pore complex appears ''donutlike'' with a massive, approximately 18 nm high annulus surrounding the membrane pore. In contrast, the nuclear face of the pore complex 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 distally by a terminal ring, thus forming a ''basket'' or ''fishtrap.'' In addition, we were able to visualize distinct structural changes occurring upon mechanical manipulation of the nuclear pore complex periphery with the scanning tip. These preliminary data provide us with the intriguing future possibility to directly correlate NPC structure with function.