Résumé : When reticulocyte polyribosomes are dissociated by EDTA treatment, two ribonucleoproteins are released: one of these, messenger ribonucleoprotein, contains the messenger RNA for globin chains and two heavy proteins (molecular weights 130 000 and 68 000); the other contains the 5 S ribosomal RNA and a lighter protein (molecular weight 45000). The protein moiety of the messenger ribonucleoprotein is required for the binding of the mRNA to deoxycholate‐washed native 40 S ribosomal subunits. Copyright © 1971, Wiley Blackwell. All rights reserved