Electron Microscopic Study of Negatively Stained Ribosomal Subunits from Geotrichum candidum

The fine structure of negatively stained, unfixed Geotrichum candidum ribo-somal subunits were observed under electron microscope. On the large subunit (60 S) three kinds of typical images were observed i.e., skiff shaped images (250 X ~220 A) which had a protrusion (~70 A) at the end of the surface, crown or maple-leaf shaped images (250 x ~ 260 A) also had a protrusion ( ~ 7 3 A) at the center of surface, and round shaped images (240 x 240 A) of which some images had a dense line at the center of subunit. On the small subunit (40 S), slightly curved elongated ellipsoidal images (270 x 130 A) and almost straight elongated ellipsoidal images (270x110 A) were obtained. The images were frequently observed as asymmetrical images. The protrusion on the large subunit was never observed on the images of monomer particles after reassociation of large and small subunits, except for the rear image. Therefore it is assumed that the protrusion should serve as a specific binding site between large and small subunits