Volume 77, number 2 FEBS LETTERS May 1977 zyxwvutsr CORRELATION OF SPECIFIC CODING SEQUENCES WITH SPECIFIC PROTEINS ASSOCIATED IN UNTRANSLATED CYTOPLASMIC MESSENGER RIBONUCLEOPROTEIN COMPLEXES OF DUCK ERYTHROBLASTS Alain VINCENT, Olivier CIVELLI, Jacques-Frangois BURI and Klaus SCHERRER zyxwvutsrqponmlkjih Service de Biochimie de la Diff&enciation, Institut de Recherche en Biologic M oltculaire, Paris, France Received 3 March 1977 1. Introduction Cytoplasmic messenger RNA exists in animal cells in the form of two types of mRNA-protein (mRNP) complexes: in polyribosomes containing the actively translated mRNA, and as free cytoplasmic mRNP with untranslated mRNA. In the case of globin mRNA, these complexes were isolated and purified as a ‘15 S’ particle from polyribosomes and as ‘20 S’ free mRNP; we found that these two different functional forms of globin mRNP contain two extensively different sets of accompanying proteins [ 11. Recently, we could demonstrate that the 20 S globin mRNA is untranslatable in vitro prior to deproteinization whereas, in contrast, the 15 S globin mRNP from polyribosomes is as readily trans- latable in vitro as the purified 9 S globin mRNA isolated from 20 S or 15 S particles-[2]. This Abbreviations: 9 S mRNA, mRNA containing globin mRNA sequences; mRNP, messenger ribonucleic-acid-protein complex; 15 S * mRNP, polyribosomal mRNP containing 9 S mRNA; 20 S* mRNP, free cytoplasmic mRNP containing globin sequences; 30 S* mRNP, free cytoplasmic mRNP containing non-globin mRNA sequences; SDS, sodium dodecyl sulfate; EDTA, ethylene diamino tetra-acetate disodium salt; M,, apparent molecular weight of proteins in SDS. * Sedimentation values are nominal only Correspondence to: Klaus Scherrer, Service de Biochimie de la Diffirenciation, Institut de Recherche en Biologie Moleculaire, Universiti de Paris 7 - Tour 43, 2, Place Jussieu, F-75221 Paris Cedex 05, France North-Holland Publishing Company - Amsterdam represents a biochemical demonstration of the concept of ‘Informosomes’ as ‘masked forms of mRNA’ proposed by Spirin [ 171. The 15 S polyribosomal mR.NP contains the same two major proteins of approximately 50 000 and 75 000 daltons found associated with polyribosomal mRNA in many different cell systems [3-51. In addition, we found 6 minor proteins [6]. It is unknown, so far, if these are specific to globin mRNA or if they are associated with all other types of mRNA as well. Differential stability, as found for example in the case of duck 9 S globin mRNA and 12 S mRNA [7] and regulation of mRNA in animal cells, calls theoretically for a mechanism of specific mRNA recognition; the mRNA associated proteins could possibly serve such a function [8]. Therefore we isolated, in addition to the pure globin 20 S free RNP, some 25-35 S free mRNP particles containing 12-14 S mRNA coding for two proteins of 22 000 and 26 000 daltons. We show here that globin mRNA and these 12-14 S mRNAs are associated with different sets of major and minor proteins in the mRNP complexes. The published 20 S protein composition [l] is confnmed and we show that these mRNP complexes are free from soluble cytosol and ribosomal proteins. Thus, an experimental basis is given to postulate recognition of specific mRNA by specific proteins at the informosome level thereby satisfying a theoretical requirement of post-transcriptional regulation at cytoplasmic level [9]. 281