Nuclease Degradation and the Structure of Ribosomes

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Abstract
Well‐defined patterns of fragments are produced when Escherichia coli ribosomes, both native, dissociated, unfolded, and partially denuded of proteins by treatment with caesium chloride, are digested with pancreatic ribonuclease, and the extracted RNA is fractionated by polyacryl‐amide gel electrophoresis. Procedures are given for determining the degree of congruence of a pair of digestion patterns, and analysing the results in terms of probability of matching. By this means it has been established that all the digestion patterns which have been obtained are closely related. The similarity between native 70‐S ribosomes and completely unfolded nucleo‐protein particles in EDTA indicates that the greater part of the RNA is accessible on the surface of the 70‐S ribosome. It has not been possible to show a close relationship between the patterns generated by the nucleoprotein particles in various states and these from free ribosomal RNA. We infer that a number of the labile points in the RNA are protected by bound proteins. The digestion proceeds much more slowly with increasing stabilisation of structure by magnesium ions, both in free RNA and ribonucleoprotein. It is shown that the labile points of the chain are segments of some length, and not isolated phosphodiester links.