Interferometric and photometric measurements have been made on replicating embryo mouse cell cultures. From a study of the relations between successive physical measurements on individual cells, it was found that the net syntheses of DNA, nuclear RNA, nuclear protein, and cytoplasmic RNA are closely associated during interphase. In auxiliary experiments, an inhibition of the onset of DNA synthesis (produced by a dose of X-rays) was found to block the majority of the accumulation of nuclear protein and nuclear RNA. These results are consistent with others previously reported in dividing cell cultures freshly prepared from normal tissues.

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