Some Properties of Ribosome Crystals Isolated from Hypothermically Treated Chick Embryos

Abstract

Ribosome crystals observed in hypothermically treated chick embryos exist as large dense aggregates and, for this reason, could be purified from a post-nuclear supernatant by centrifugation through a high-density discontinuous sucrose gradient. A ribosome crystal fraction isolated in this way was observed, by electron microscopy, to contain intact crystals, resembling those seen in sectioned whole cells, with only minor contamination from morphologically indistinct particles. The ribonucleic acid (RNA) content of this fraction was found to be the same as ribosomal RNA from mature chickens. However, their resistance to mild RNase treatment, lack of transfer RNA and endogenous messenger RNA activity indicate that such ribosome crystals are not a specific type of polysome. The intertetramer bonds (i.e. bonds between tetramers in a crystal array) are much more susceptible to mild protease treatment than to treatment with ribonuclease (RNase), indicating a dependence on protein-protein interactions for their formation.