Ribosome crystals in necrotizing cells from the posterior necrotic zone of the developing chick limb

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Abstract
Ribosome and ‘protein crystals’ were observed in electron micrographs of degenerating cells from the posterior necrotic zone (PNZ) of developing chick limbs, stages 22 through 24. Ribosome crystals were made up of basic units of 4 ribosomes arranged in a square tetramer. They were monomorphic with the surface lattice being of the p4 plane group. The 1-ribosome thick sheets of crystals were often seen stacked upon one another forming a 3-dimensional P422 configuration. The percentage of crystallized ribosomes within degenerating PNZ cells is nearly directly proportional to the degree of degeneration of the cell. Crystals identical to this have been observed in numerous types of embryonic chick cells subjected to hypothermia. The ‘protein crystals’ were composed of straight filamentous structures separated by a distance of 20–30 nm. They were always closely associated with the ribosome crystals. These crystals are similar to those seen in cells treated with high doses of vinblastine and vincristine. The pathogenesis of the ribosome and protein crystals occurring in degenerating PNZ cells is unknown. They are not associated in any way with hypothermia or vinblastine-vincristine treatment.