An endomessenger hypothesis on the mechanism of information transfer in animal cells

Abstract

Research on the mechanism of information transfer in animal cells is reviewed. It is indicated that the interpretation of experimental results within the framework of the original messenger concept leads to several fundamental controversies. The most important concern the nature of: (a) the rapidly-labelled 45 s nuclear RNA; (b) the cytoplasmic 40 s ribonucleoprotein particle; and (c) the nuclear and cytoplasmic 18 s RNA's. In order to explain the available facts and to avoid the controversies in their interpretation, a new hypothesis is proposed, designated as the endomessenger hypothesis. The main feature of the advanced hypothesis is the consideration of “messenger” RNA's as an integral part of some cellular “ribosomal” RNA's, namely, the “ribosomal” precursor 45 s RNA and the “ribosomal” 18 s RNA. The experimental evidence and the theoretical grounds are discussed, primarily focused on: (a) the synchronous formation and turnover of the two ribosomal subunits and their RNA's correlated with the stability of messenger RNA's in animal cells; (b) the existence of RNA molecules with a hybrid mononucleotide composition, constituted of a “ribosomal” segment and a “messenger” segment; (c) the vectorial transcription of the genome, involving one of the two DNA strands, initiated from the “ribosomal” RNA segments and finished with the “messenger” RNA segments; and (d) the relatively extended time period necessary for the completion of any RNA molecule. The implications derived from the proposed endomessenger hypothesis, on the mechanism of information transfer in animal cells are discussed.