Ribosome substructure investigated by scanning force microscopy and image processing

Scanning force microscopy was used to study the ultrastructure of eukaryotic ribosomes from Chironomus pallidivittatus in the polysomal complex. Positively stained polysomes were imaged, and the resulting three-dimensional ribosomal structures were further processed by statistical analyses of virtual cross-sections parallel to the substrate plane. Structural investigations were based on parameters which are minimally influenced by the tip geometry, like section plane centre or axis ratio. In the lower part of the structure a shift of the section centres was observed, suggesting an attached structure. The geometry of the sections revealed an elliptical shape in the upper part (axis ratio 1.52 ± 0.22), with a less elongated shape in the lower region (axis ratio 1.41 ± 0.18). A model for the surface topography of a positively stained ribosome exhibiting a small subunit attached along the long side of an elliptical large structure is proposed.