The nucleic acids-metabolic key to development?

Abstract

Highly purified preparations of RNA prepared from mature ovarian eggs of Rana catesbeiana contain at least two gross fractions of RNA: one that is soluble in cold 0.5 M perchloric acid (acid-soluble RNA) and another that is insoluble in the same concentration of acid (acid-insoluble RNA). Each Comprises roughly 50 per cent of the total RNA. The two RNA fractions are distinct not only in solubility characteristics but in nucleotide composition as well. A procedure has been developed for the mass isolation of structures morphologically similar to the nucleoli of mature ovarian eggs. These structures contain no DNA, from 8 to 17 per cent RNA, and a large amount of protein. The distribution of P32 in the mononucleotides of cytoplasmic RNA, nuclear RNA, and nucleolar RNA shows that the mononucleotide compositions, based on counts, of nuclear RNA and nucleolar RNA are essentially the same. Nucleolar RNA apparently contains a major component (compound X) which superficially resembles uridylic acid and may be pseudouridylic acid. That RNA is indeed active in a differentiation process is evidenced by the rapid increase in the rate of incorporation of P32 into liver RNA during induced metamorphosis. This response is among the earliest recorded for induced metamorphosis and precedes the increase in activity of many liver enzymes.