Synthesis and accumulation of DNA-like RNA during embryogenesis of Xenopus laevis

Abstract

A technique has been developed which quantitates the DNA-like RNA (dRNA) which is synthesized during embryogenesis of the amphibian Xenopus laevis. The technique utilizes [ 32P]phosphate as a precursor and relies on the fact that the synthesis of ribosomal RNA is low compared to that of dRNA for a considerable period of early embryogenesis. Radioactivity in dRNA at each stage has been converted into dRNA content by measuring the specific activities of the α-phosphates of RNA precursors in the acid-soluble pool and assuming that they are the same as the specific activity of the dRNA. The results show that a mature oocyte synthesizes about 1 to 6 mμg of [ 32P]dRNA during ovulation, an amount equal to about 0.02 to 0.1% of the total RNA in the egg. During development, the content of [ 32P]dRNA in embryos increases relative to ribosomal RNA until about 2% of the total RNA in swimming embryos is [ 32P]dRNA. During early embryogenesis when dRNA increases relative to ribosomes, the content of [ 32P]dRNA in the embryo approximately doubles with each doubling of the DNA content.