Non-coordinate synthesis of division-related mRNA.

AMINO-ACIDS are thought to control the rate of RNA synthesis in bacteria1. In a series of preliminary experiments we showed that amino-acids strongly influence the rate of uptake of labelled RNA precursors in synchronized Tetrahymena, a eukaryotic ciliated protozoan2. It was especially interesting to examine the nature of the RNA synthesized in these conditions for two reasons: (a) synchronized Tetrahymena can divide without net RNA synthesis2 and (b) there is considerable evidence suggesting that template RNA must be synthesized between the end of the synchronizing treatment and the first synchronous division3. Because evidence has been accumulating from both bacterial and mammalian cell systems to indicate that neither isotope uptake4 nor hybridization5 techniques can accurately measure the rate of mRNA synthesis, other means of assaying its rate of synthesis in various circumstances would be useful. The precision of timing of synchronous division in Tetrahymena6 therefore appeared to offer a unique assay for mRNA synthesis. Our results suggest that the complete absence of amino-acids in the media does not significantly affect the rate of division-related mRNA synthesis in Tetrahymena.