Effects of γ-irradiation on the synthesis of ribosomal RNA and on the concomitant formation of ribosomal subparticles in Escherichia coli cells were studied. The amount of RNA species synthesized was exponentially decreased with increasing doses. While the size of these RNA molecules was nearly normal and accumulation of prematurely terminated molecule was not detected, a larger amount of the RNA species having sedimentation coefficients of 17 S and 23.5 S was present in irradiated cells than was in unirradiated control cells. This was accounted for by the retardation of the maturation process from the precursor form to the mature form. The sequential assembly of ribosomal subparticles was also delayed by irradiation. This retardation was more prominent in the formation of 50 S subparticles than in the formation of 30 S. It was concluded that irradiation affects the synthesis of rRNA and ribosomal particles in a similar fashion as do antibiotics or starvation of amino acids.

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