title: Free cytoplasmic messenger ribonucleoprotein complexes from rabbit reticulocytes.
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 alpha-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.
mesh_terms: D000818:Animals; D005260:Female; D005914:Globins / Q000096:biosynthesis; D006427:Hemin / Q000494:pharmacology; D008970:Molecular Weight; D009698:Nucleoproteins / Q000097:blood*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D012333:RNA, Messenger / Q000097:blood*; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000097:blood*; D014981:Xenopus
chemical_list: D009698:Nucleoproteins; D012333:RNA, Messenger; D012261:Ribonucleoproteins; D006427:Hemin; D005914:Globins