Traduction de l'acide ribonucléique messager en hémoglobine

Abstract

Definition of mRNA. Jacob and Monod have suggested that mRNA should possess five properties. Nevertheless mRNA reflects the composition of only a very small fragment of DNA and its renewal is not always fast. Moreover, mRNA should be able to direct the synthesis of a specific protein. Demonstration of translation of RNA into hemoglobin. We can observe : a) The labelling of hemoglobin. It is unsufficient because of the possible presence of small amount of highly radioactivity impurity. b) The labelling of isolated α or β chain, which is a better method. It was used by Lockard and Lingrel with RNA from mice in rabbit and duck systems, with a demonstration of mice β chain synthesis [1969–1970]. Anderson performed the synthesis of α and β chain of rabbit onto human ribosomes [1971]. c) The labelling of specific peptides obtained by digestion. This is the best method in our opinion : two varieties of α hemoglobin have been found in rabbit, one with αTIV leu, one with αTIV val ; using mRNA from one variety and ribosomes from the other, the added as well as the endogenous mRNA is translated as demonstrated by the labelling of the specific peptides [1968, Schapira, Dreyfus and Maleknia]. On the other hand the translation of mRNA of rabbit hemoglobin onto E. coli ribosomes has not been confirmed. Heywood claimed that he has observed a translation of mRNA from hemoglobin onto embryonic muscle ribosome and of mRNA from myosin onto reticulocyte ribosomes. Specificity of initiation factors and of ribosomal protein. No specificity of initiation factors on hemoglobin synthesis have been found in rabbit, guinea pig [Schapira, Reibel and Cuault] and human [Anderson et al.] reticulocytes. Conflicting with the classical point of view, we found that some ribosomal proteins are different in various tissues of the same species [Huynh Van Tan, Delaunay and Schapira]. The signification of these observations is discussed. Regulation of biosynthesis of α and β chains. There is good evidence that free α chain is able to combined with β chain still attached to ribosomes [Baglioni]. We give new evidence of this mechanism and demonstrate the specific role of α chain [Blum, Maleknia and Schapira].