Unstable Structure of Ribosomal Particles Synthesized in γ-irradiated Escherichia coli

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Stability of Escherichia coli ribosomes newly synthesized after γ-irradiation was compared with that of normal ribosomes. The ribosomal particles around 70-S synthesized in irradiated cells were more sensitive to digestion by pancreatic ribonuclease A. There existed a higher amount of the salt-unstable '50-S' precursor particles in the extract from irradiated cells than in the extract from unirradiated cells. These facts suggest that ribosomal particles synthesized during an earlier stage in irradiated cells maintain an incomplete structure, even though they are not distinguishable from the normal ribosomes by means of sucrose density-gradient centrif ugation. Bacterial ribosomal subparticles are built up in stepwise fashion assembling a set of ribosomal proteins. In the previous study, we observed that γ-irradiation of Escherichia coli reduced the conversion rate of the ribosornal biosynthetic intermediates to the mature subparticles and that the irradiation also retarded the maturation from the precursor RNA to the mature form. It is of interest to exarnine whether ribosomal particles which are synthesized in γ-irradiated Escherichia coli cells have the normal internal structure.
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