Ribonucleic acid synthesis in embryonic chick muscle, rates of synthesis and half-lives of transfer and ribosomal RNA species.

In this study the term 'rates of synthesis' does not refer to rates of transcription but to rates of accumulation of newly synthesized RNA. The rates of synthesis and half-lives of tRNA, 18S and 28S rRNA of 14-day and 17-day embryonic chick muscle were determined by following the accumulation of radioactive AMP in RNA after administration of [3H]8-adenosine to chick embryos and correcting for the average specific activity of the precursor ATP pool Transfer RNA of 14-day embryonic chick muscle is synthesized at a rate of 2.4 x 10(5) molecules per min per 2N DNA content and decays with a half-life of 50h. Transfer RNA of 17-day embryonic chick muscle is synthesized, and decays, at similar rates. Ribosomal RNA, 18S and 28S, are synthesized at a rate of 9.94 x 10(3) and 8.48 x 10(3) molecules per min per 2N DNA, respectively, in 14-day embryonic chick muscle. The rates of rRNA syntheis in 17-day embryonic muscle are also similar. In both 14-day and 17-day embryonic muscle, 18S and 28S rRNA each decays with a half-life of 65h. We conclude that the constant level of tRNA and rRNA in embryonic chick muscle from 14 to 17 days (Nwagwu & Nana, 1974) is maintained also by a constant rate of synthesis and turnover.