A conserved role of a DEAD box helicase in mRNA masking.
Clam p82 is a member of the cytoplasmic polyadenylation element-binding protein (CPEB) family of RNA-binding proteins and serves dual functions in regulating gene expression in early development. In the oocyte, p82/CPEB is a translational repressor, whereas in the activated egg, it acts as a polyadenylation factor. Coimmunoprecipitations were performed with p82 antibodies in clam oocyte and egg lysates to identify stage-regulated accessory factors. p47 coprecipitates with p82 from oocyte lysates in an RNA-dependent manner and is absent from egg lysate p92-bound material. Clam p47 is a member of the RCK/p54 family of DEAD box RNA helicases. Xp54, the Xenopus homolog, with bona fide helicase activity, is an abundant and integral component of stored mRNP in oocytes (Ladomery et al., 1997). In oocytes, clam p47 and p82/CPEB are found in large cytoplasmic mRNP complexes. Whereas the helicase level is constant during embryogenesis, in contrast to CPEB, clam p47 translocates to nuclei at the two-cell stage. To address the role of this class of helicase in masking, Xp54 was tethered via 3' UTR MS2-binding sites to firefly luciferase, following microinjection of fusion protein and nonadenylated reporter mRNAs into Xenopus oocytes. Tethered helicase repressed luciferase translation three- to fivefold and, strikingly, mutations in two helicase motifs (DEAD--> DQAD and HRIGR-->HRIGQ), activated translation three- to fourfold, relative to MS2. These data suggest that this helicase family represses translation of maternal mRNA in early development, and that its activity may be attenuated during meiotic maturation, prior to cytoplasmic polyadenylation.
Minshall
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Department of Biochemistry, University of Cambridge, United Kingdom.
Thom
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Standart
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D000595:Amino Acid Sequence; D000818:Animals; D049872:Bivalvia / Q000201:enzymology / Q000235:genetics*; D017124:Conserved Sequence; D005786:Gene Expression Regulation; D008969:Molecular Sequence Data; D005810:Multigene Family; D009865:Oocytes / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis; D011500:Protein Synthesis Inhibitors; D011518:Proto-Oncogene Proteins; D020365:RNA Helicases / Q000235:genetics / Q000378:metabolism*; D012316:RNA Nucleotidyltransferases; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D011500:Protein Synthesis Inhibitors; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; C026452:messenger ribonucleoprotein; C117068:p82 protein, clam; D012316:RNA Nucleotidyltransferases; D020365:RNA Helicases