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Reticulocyte ribosomes from one species when incubated with a soluble reticulocyte fraction from another species have been shown to synthesize the haemoglobin of both species. This result supplies evidence for the presence of a messenger in the non-particulate fraction and the possible fixation of this messenger on the ribosomes of the first species. The incubation system is made of cell-free fractions from rabbit and guinea pig reticulocytes. The synthesized haemoglobins are located by double intermolecular labelling. Carrier haemoglobin, labelled with a tracer different from that used during the incubation, is added before separation of the haemoglobins. The haemoglobins are identified by isolating species-characteristic tryptic peptides containing tyrosine. The absence of any ribosomal contamination in the soluble fraction is proved. The nature and action of the active principle lead to its identification as a messenger RNA. The non-specificity of the ribosomes versus mRNA is at present accepted as a result of work with synthetic polynucleotides. The attempts to demonstrate a specific action of natural messenger on ribosomes from other species have often led to equivocal results. Our experiments, while confirming the lack of ribosomal specificity in the case of cell-free systems from rabbit and guinea pig reticulocytes, raise questions about the limits of this non-specificity.

Publisher Summary This chapter describes the methods for the identification of peptides during hemoglobin biosynthesis and measurement of their sequential synthesis. A model of protein synthesis by sequential growth whereby amino acids are joined one after the other down a polypeptide chain is postulated. Taking hemoglobin as an example, it is demonstrated that peptide chains grow by serial addition of amino acids, starting at the free amino terminal and going toward the free carboxyl terminal. A method of preparative analysis chromatography of amino acids is described in the chapter that allows the determination of specific radioactivity on any number of amino acids at once in protein biosynthesis studies. The general technical procedure presents an adaptation of paper chromatography and paper electrophoresis procedures for the isolation and characterization of tryptic peptides of hemoglobin. Another new technique is ion-exchange chromatography with volatile organic developers, which appears to have a considerably higher resolving power than paper electrophoresis. Electrophoresis on filter paper strips provides a method of separating peptides in an electric field.