Ribosomes derived from the sulfur-dependent archaebacteria are structurally distinct from those types found in ribosomes from eubacteria, eukaryotes, and other archaebacteria. All four ribosome types share a common structural core, but each type also has additional independent structural features. In the smaller subunit derived from sulfur-dependent archaebacteria ("eocytes"), lobes, similar to those found at the base of the eukaryotic small subunits, and an archaebacterial bill, similar to those found on the smaller subunit of archaebacteria and eukaryotes, are present. On the larger subunit from sulfur-dependent archaebacteria, an eocytic lobe, eocytic gap, and eocytic bulge are present. These features, with the exception of the eocytic gap, are found in a slightly modified form on eukaryotic large subunits. These novel ribosomal properties are in general consistent with other molecular biological properties peculiar to these organisms.

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