Free cytoplasmic messenger ribonucleoprotein complexes from rabbit reticulocytes |
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Authors: | Hans M. G. Princen Chris A. G. van Eekelen Fred A. M. Asselbergs Walther J. van Venrooij |
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Affiliation: | (1) Department of Biochemistry, University of Nijmegen, Geert Grooteplein Noord 21, Nijmegen, The Netherlands |
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Abstract: | Free cytoplasmic globin mRNA containing mRNP-particles were isolated from rabbit reticulocytes by zonal sucrose gradient centrifugation and their properties were compared with mRNP particles isolated in the same way from EDTA-dissociated reticulocyte polyribosomes. The average poly(A)-length of 9S mRNA from free cytoplasmic mRNP was 17–20 nucleotides being about two times shorter than the average poly(A)-length of polysomal 9S mRNA. The protein composition of the free cytoplasmic mRNP particles disclosed the absence of the 76,000 dalton protein which is associated with the 3 poly(A)-segment of polysomal globin mRNA. It was concluded that free cytoplasmic mRNP-particles from rabbit reticulocytes can be classified as old mRNP in a post-translational phase. Free cytoplasmic mRNPs were translated in heterologous cell-free systems as well as in Xenopus laevis oocytes. Addition of hemin stimulated the synthesis of -globin in all systems, while the presence of the cap analogue m7G(5 )p inhibited translation of free cytoplasmic mRNA completely. The latter finding suggested that free cytoplasmic mRNA has a 5 terminal cap . Shortening of the poly(A)-segment with concomitant loss of the 76,000 dalton protein may lead to less efficient translation of free cytoplasmic mRNP. |
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