title: Sequences mediating the translation of mouse S16 ribosomal protein mRNA during myoblast differentiation and in vitro and possible control points for the in vitro translation.
abstract: The translation of ribosomal protein (r-protein) mRNAs is generally inefficient and regulated during the differentiation of mouse myoblasts into fibers. In this discussion we show that the first 31 nucleotides of the S16 r-protein mRNA, when located at the 5' end of the mRNA, are sufficient to impart the translational properties of an r-protein mRNA to the SV-GALK mRNA, which is normally translated efficiently in both myoblasts and fibers. If the same S16 sequences are located within the interior of the 5'-untranslated region of the SV-GALK mRNA, however, they do not impart the translational properties of an r-protein mRNA to the SV-GALK mRNA. The translation of mouse r-protein mRNAs was examined in vitro to help elucidate the mechanisms controlling their translation. Mouse r-protein mRNAs are inefficiently translated in rabbit reticulocyte extracts, and the same sequences that mediate their inefficient and regulated translation during myoblast differentiation also mediate their inefficient translation in a position-dependent manner in reticulocyte extracts. To determine whether the subpolysomal r-protein mRNAs that are not actively translated in vivo are capable of translation, subpolysomal RNA was translated in reticulocyte extracts. The subpolysomal r-protein mRNAs are just as capable of translation as are polysomal mRNAs. To help identify the initiation factors and/or the steps in the initiation pathway that mediate the inefficient translation of r-protein mRNAs, reticulocyte extracts were supplemented with purified initiation factors. Only eIF-4F, the cap-binding complex, and eIF-3, which is involved in subunit dissociation and interacts with eIF-4F during initiation, stimulated the translation of r-protein mRNA. These experiments, along with m7GDP inhibition studies, suggest that eIF-4F and/or eIF-3, or the steps mediated by these factors, mediate the inefficient translation in reticulocyte extracts and raise the possibility that these steps also control the regulated translation of r-protein mRNAs during myoblast differentiation.
authors.affiliation: Department of Biological Sciences, University of South Carolina, Columbia 29208.
authors.forename: M L
authors.initials: ML
authors.lastname: Hammond
authors.forename: W
authors.initials: W
authors.lastname: Merrick
authors.forename: L H
authors.initials: LH
authors.lastname: Bowman
mesh_terms: D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation / Q000235:genetics; D002460:Cell Line; D039621:Eukaryotic Initiation Factor-3; D039562:Eukaryotic Initiation Factor-4F; D006153:Guanosine Diphosphate / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D024510:Muscle Development; D009132:Muscles / Q000166:cytology*; D010448:Peptide Initiation Factors / Q000378:metabolism; D010957:Plasmids; D014176:Protein Biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism*; D012156:Reticulocytes / Q000378:metabolism; D012261:Ribonucleoproteins / Q000235:genetics; D012269:Ribosomal Proteins / Q000235:genetics* / Q000378:metabolism; D014162:Transfection
chemical_list: D039621:Eukaryotic Initiation Factor-3; D039562:Eukaryotic Initiation Factor-4F; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D012261:Ribonucleoproteins; D012269:Ribosomal Proteins; C023509:ribosomal protein S16; D006153:Guanosine Diphosphate