Nuclear pores are large
protein complexes which cross the
nuclear envelope, the
membrane surrounding the
eucaryotic cell nucleus. There are about 3.000 nuclear pore complexes on the nuclear envelope of an animal cell. They allow the transport of water-soluble molecules across the nuclear envelope. Each of the eight protein subunits surrounding the actual pore (the outer ring) projects a spoke-shaped protein into the pore channel. The center of the pore often contains a plug protein of yet unknown structure.
Image from [Nupedia server