摘要：

The established cell lines 3T6 and 3T3 contain more of both rRNA and mRNA when they are growing than when they are resting, but mRNA is increased more than rRNA. During conversion of 3T6 cultures from resting to growing state, mRNA, rRNA, and tRNA accumulate long before DNA synthesis begins. The increases in rRNA and tRNA are coordinate, but mRNA accumulates earlier and to a greater extent than the others. The rate of protein synthesis in cultures in transition from resting to growing state increases faster than their content of rRNA and appears proportional to the amount of mRNA rather than to the number of ribosomes. The doubling of mRNA content that takes place before any cells begin to synthesize DNA should be considered in relation to the absence of change in the overall rate of synthesis of HnRNA during the same period.

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