The specificity of interaction between mRNP proteins and globin mRNA in polyribosomal and cytoplasmic free mRNP.
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Biomedical subjects
Publications and source records attributed to S Goldenberg.
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EDTA dissociation of polyribosomes from duck erythroblasts allowed us to isolate the 15-S globin messenger ribonucleoproteins (mRNP) by sucrose gradient centrifugation or affinity chromatography on poly(U)-Sepharose or oligo(dT)-cellulose columns. Their protein composition was compared by one and two-dimensional electrophoresis in sodium dodecyl sulfate to the free 20-S mRNP containing the repressed fraction of globin mRNA [Vincent, A., Civelli, O., Maundrell, K., and Scherrer, K. (1980) Eur. J. Biochem. 112, 617--633]. The protein composition of the 15-S mRNP isolated by these methods in different ionic strength conditions, was characterized by a major 73 000-Mr polypeptide and seven minor polypeptides with Mr ranging from 45 000 to 68 000, all of which are slightly basic, and about five acidic ones in the 80 000--130 000-Mr range. All these are retained in the 15-S mRNP core particle isolated at 0.5 M KCl. At low ionic strength, in addition, a specific group of acidic polypeptides in the Mr range 35 000--105 000 was also found associated with globin mRNA. Oligo(dT)-cellulose chromatography of mRNP digested with ribonucleases A and T1 indicated that the 73 000-Mr major protein is bound to the poly(A) segment; some other proteins resolved as minor components interact with both the poly(A) and non-poly(A) regions of globin mRNA. Characterization of proteins interacting with the poly(A) segment of non-polyribosomal globin mRNA in 20-S free mRNP demonstrated the absence of the polyribosomal 73 000-Mr poly(A)-binding protein. Furthermore, it confirmed that the protein compositions of translatable polyribosomal and repressed free globin mRNP are very different. Indeed, the respective core (0.5 M KCl) particles contain only two possibly common polypeptides. The specificity of proteins associated with globin mRNA in two different functional states shown here supports the hypothesis of a role of mRNP proteins in translational control of mRNA.
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The study of the interaction between mRNA and proteins in the polyribosomal 15 S duck globin messenger ribonucleoprotein complex showed that proteins protect specific mRNA sequences against digestion by the nonspecific micrococcal nuclease (Nucleic Acids Research 6 (8) 2787, 1979). Here we report the isolation of the poly(A)-protein RNP complex from nuclease digested 15 S mRNP by two different methods: sucrose gradient sedimentation and oligo(dT)-cellulose chromatography. We show by fingerprint analysis, that aprt from the periodically fragmented poly(A) segment, mRNA sequences adjacent and non-adjacent to the poly(A) segment are protected by the poly(A) binding proteins against nuclease digestion. The duck globin poly(A)-protein RNP complex, with a sedimentation coefficient between 7 S and 10 S, shows a characteristic protein composition, with a major 73,000 MW polypeptide and some minor components. The results are discussed in view of a dynamic ribonucleoprotein structure.
A comparison of the organization of six avian adult globin messenger sequences is based on previously reported recombinant duck adult globin cDNA plasmids (Therwath et al., 1980) and the actual construction and characterization of pBR322 recombinant plasmids including the beta and the normal alpha A and alpha D chicken adult globin mRNA sequences. Identification of the cloned DNA was performed using hybridization-selection under conditions permitting complete purification in one step of the three globin mRNAs, and translation of the corresponding mRNA. Orientation of the globin insert in the vector was determined, taking into account the computer prediction of the restriction sites based on the known amino acid sequences of the three globin chains (Roizès and Pelaquier, 1980) and those actually observed, and by identification of restriction fragments using 3'-specific probes. Identification, orientation and restriction mapping of these cloned DNAs reveals extensive homologies in organisation of beta sequences between duck and chicken, as well as among the alpha sequences in every two possible combinations.
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Purified 15 S globin mRNA-protein (mRNP) complexes obtained by EDTA dissociation of duck reticulocytes polyribosomes were digested with the calcium dependant Staphylococcus aureus nuclease (EC 3. 1. 4. 7.). 25% of the globin mRNA sequences were resistant to extensive nuclease digestion as determined by TCA precipitation of the digested 15 S particles labelled in vivo with tritiated uridine. Polyacrylamide gel electrophoresis of the RNA from nuclease digested 15 S particles showed that the protected oligoribonucleotides were distributed into two distinct size classes of 25,000 and 12,000 MW. Comparison between in vitro iodine-labelled 9 S globin mRNA extracted from Staphylococcal nuclease digested 15 S mRNP particles was carried out by fingerprinting. Mapping of T1 ribonuclease digests by high-voltage electrophoresis and homochromatography showed that specific oligoribonucleotides were protected against nuclease attack by proteins of the 15 S mRNP.
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Duck- and rabbit globin messenger ribonucleoprotein complexes isolated by oligo(dT) cellulose chromatography reveal an identical protein pattern-two main proteins of molecular weights of 73,000 and 49,000 daltons and minor components-whether the complexes have been liberated from polyribosomes with the EDTA- or the puromycin-high-salt method. In the globin messenger ribonucleoprotein particles of both species predominantly the protein with a molecular weight of 73,000 daltons is attached to poly(A)-containing regions of the messenger RNAs.
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