Some electron microscopic studies on intact nuclear 'ghosts' and nuclear membrane fragments

Abstract
The electron optical images of negatively stained intact nuclear ‘ghosts’ are readily identified as flattened and sometimes folded bodies, not unlike those given by mammalian erythrocyte ‘ghosts’. Even at low magnifications ( x 5000) the nuclear pore complexes are clearly revealed and can therefore be used as morphological markers for nuclear membrane. At higher magnifications the nuclear pore complexes are seen to be composed of an eight-sided annulus surrounding a central granule, an inner ring of material, and possibly radial fibrils. Very often fine detail appears to be obscured owing to the fact that there are two layers of double nuclear membrane lying flat on the carbon support film. Occasionally the nuclear ‘ghosts’ appear to be torn apart, in all probability because of the spreading and surface-tension forces applied during the preparation of the negatively stained specimens. In this instance the nuclear pore complexes usually remain intact and the surrounding membrane is disrupted. The nuclear pore complexes are spread as a single layer and greater detail is revealed within the annuli. This is particularly so when partially disrupted nuclear pore complexes are studied. The octagonal annulus appears to be composed of circular macromolecules approximately 20 nm in external diameter with a 5 nm diameter central hole. These macromolecules are linked together and partly masked by other diffuse material. It is proposed that one or more of these macromolecules underlies each of the eight annular subunits. A model for the nuclear pore complex is presented and compared with those proposed by other authors.

This publication has 0 references indexed in Scilit: