title: RAP55, a cytoplasmic mRNP component, represses translation in Xenopus oocytes.
abstract: mRNAs in eukaryotic cells are presumed to always associate with a set of proteins to form mRNPs. In Xenopus oocytes, a large pool of maternal mRNAs is masked from the translational apparatus as storage mRNPs. Here we identified Xenopus RAP55 (xRAP55) as a component of RNPs that associate with FRGY2, the principal component of maternal mRNPs. RAP55 is a member of the Scd6 or Lsm14 family. RAP55 localized to cytoplasmic foci in Xenopus oocytes and the processing bodies (P-bodies) in cultured human cells: in the latter cells, RAP55 is an essential constituent of the P-bodies. We isolated xRAP55-containing complexes from Xenopus oocytes and identified xRAP55-associated proteins, including a DEAD-box protein, Xp54, and a protein arginine methyltransferase, PRMT1. Recombinant xRAP55 repressed translation, together with Xp54, in an in vitro translation system. In addition, xRAP55 repressed translation in oocytes when tethered with a reporter mRNA. Domain analyses revealed that the N-terminal region of RAP55, including the Lsm domain, is important for the localization to P-bodies and translational repression. Taken together, our results suggest that xRAP55 is involved in translational repression of mRNA as a component of storage mRNPs.
authors.affiliation: Laboratory of Cellular Biochemistry, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
authors.forename: Kimio J
authors.initials: KJ
authors.lastname: Tanaka
authors.forename: Kenji
authors.initials: K
authors.lastname: Ogawa
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Takagi
authors.forename: Naoko
authors.initials: N
authors.lastname: Imamoto
authors.forename: Ken
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Masafumi
authors.initials: M
authors.lastname: Tsujimoto
mesh_terms: D000818:Animals; D003593:Cytoplasm / Q000737:chemistry* / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism* / Q000502:physiology; D014176:Protein Biosynthesis / Q000502:physiology*; D012333:RNA, Messenger / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D034741:RNA, Small Interfering / Q000502:physiology; D016601:RNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D012261:Ribonucleoproteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D040681:Structural Homology, Protein; D014157:Transcription Factors / Q000302:isolation & purification; D029867:Xenopus Proteins / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: C516955:RAP55 protein, Xenopus; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; C510649:RNA-associated protein 55, human; D012097:Repressor Proteins; D012261:Ribonucleoproteins; D014157:Transcription Factors; D029867:Xenopus Proteins; C075593:YBX2 protein, Xenopus; C026452:messenger ribonucleoprotein