In experiments of 6 hours duration, no replacement of phosphorus or purine and pyrimidine carbon in DNA, nor flow of these atoms from RNA to DNA, could be detected in rapidly growing cultures of E. coli. The slow replacement that has been demonstrated for many substances in non-proliferating tissues of other organisms, though it may occur also in bacteria, is not greatly accelerated under conditions of rapid cellular growth, and therefore cannot be a characteristic feature of synthetic processes.

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