Abstract
THE discovery that messenger RNA (mRNA) in mammalian cells contains sequences of polyadenylic acid (poly A) about 200 nucleotides long localized at the 3′-OH terminus of the mRNA molecule1–5 has raised questions about the function of poly A, but has also provided a powerful new tool for the study of mRNA metabolism. I have measured the stability of mRNA in exponentially growing mouse L-cells without having to resort to the use of inhibitors of RNA synthesis, and found that poly A-containing mRNA has a half-life of 10 h, and thus turns over approximately once per cell generation (15 h). This high stability is in striking contrast to the 3–4 h half-life for mRNA in cultured cells obtained by following the decay of polyribosomes after treatment with a high dose of actinomycin D6,7, This, however, agrees with the finding of Cheevers and Sheinin8 that there is a long-lived fraction of mRNA in cells treated with a low dose of actinomycin D. Singer and Penman9 have simultaneously found that poly A-containing mRNA in HeLa cells turns over about once per cell generation.
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