Formation and fate of abnormal ribosomes of E. coli cells treated with 5-fluorouracil.

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Abstract
The ribonucleoprotein particles synthesized by E. coli cells in the presence of 5-fluorouracil and thymine are abnormal: (a) Their sedimentation characteristics differ from those of normal ribosomes; (b) they are less stable than the latter, both in vivo and in vitro; (c) in their RNA moiety, about 70 per cent of the uridylic acid constituent is replaced by the fluoro analogue. This abnormal RNA differs from normal ribosomal RNA in its elution from methylated albumin columns, in its behavior in sucrose gradietn centrifugation, and in its hyperchromicity when being heated. The abnormal particles have, by several criteria, been shown not to serve as the immediate precursors in the biosynthesis of ribosomes, but to be degraded in the cells, during their recovery from the action of the fluoro analogue, furnishing material for the synthesis of normal RNA and ribosomes.