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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)
 
Gene Review

smg  -  smaug

Drosophila melanogaster

Synonyms: CG5263, D69, Dmel\CG5263, Protein Smaug, SMG, ...
 
 
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High impact information on smg

  • smaug protein represses translation of unlocalized nanos mRNA in the Drosophila embryo [1].
  • Analysis of point mutations in the SREs reveals a strong correlation between smaug binding and translational repression; mutants unable to bind smaug in vitro are not repressed translationally in vivo, whereas mutants that do bind smaug remain repressed translationally [1].
  • We report here the crystal structure of the Smaug RNA binding domain, which shows no sequence homology to any previously characterized RNA binding motif [2].
  • Thus, Smaug represses translation via a Cup-dependent block in eIF4G recruitment [3].
  • Using homology modeling and site-directed mutagenesis, we have localized the RNA-binding surface of the Smaug SAM domain and have elaborated the RNA consensus sequence required for binding [4].
 

Biological context of smg

  • The same extracts show pronounced translational repression mediated by the Smaug response elements [5].
  • RESULTS: Here, we identify the RNA binding protein, Smaug, previously known as a translational repressor of nanos, as a key regulator of degradation/protection-based transcript localization [6].
  • Smaug, a novel and conserved protein, contributes to repression of nanos mRNA translation in vitro [7].
  • Repression during oogenesis and embryogenesis are mediated by distinct stem loops within the nanos 3' untranslated region; the Smaug-binding stem-loop acts strictly in the embryo, whereas a second stem-loop functions in the oocyte [8].
  • We show that both components to spatial control of nanos translation initiate during oogenesis and that translational repression is initially independent of Smaug, an embryonic repressor of nanos [8].
 

Physical interactions of smg

  • We show that the Smaug protein bound to the nanos 3' UTR recruits the deadenylation complex CCR4-NOT, leading to rapid deadenylation and subsequent decay of nanos mRNA [9].
  • Rather, Smaug physically interacts with the CCR4/POP2/NOT deadenylase, recruiting it to Hsp83 mRNA to trigger transcript deadenylation and degradation [6].
 

Regulatory relationships of smg

  • CONCLUSIONS: Smaug triggers destabilization and localization of specific maternal transcripts through recruitment of the CCR4/POP2/NOT deadenylase [6].
 

Other interactions of smg

  • These observations suggest that Smaug operates a translational switch that governs the distribution of Nanos protein [10].
  • Smaug recruits the CCR4/POP2/NOT deadenylase complex to trigger maternal transcript localization in the early Drosophila embryo [6].
  • In smaug mutants, degradation of Hsp83 transcripts is not triggered, and, thus, localization does not occur [6].
 

Analytical, diagnostic and therapeutic context of smg

References

  1. smaug protein represses translation of unlocalized nanos mRNA in the Drosophila embryo. Smibert, C.A., Wilson, J.E., Kerr, K., Macdonald, P.M. Genes Dev. (1996) [Pubmed]
  2. RNA recognition via the SAM domain of Smaug. Green, J.B., Gardner, C.D., Wharton, R.P., Aggarwal, A.K. Mol. Cell (2003) [Pubmed]
  3. Drosophila Cup is an eIF4E-binding protein that functions in Smaug-mediated translational repression. Nelson, M.R., Leidal, A.M., Smibert, C.A. EMBO J. (2004) [Pubmed]
  4. The RNA-binding SAM domain of Smaug defines a new family of post-transcriptional regulators. Aviv, T., Lin, Z., Lau, S., Rendl, L.M., Sicheri, F., Smibert, C.A. Nat. Struct. Biol. (2003) [Pubmed]
  5. Rapid ATP-dependent deadenylation of nanos mRNA in a cell-free system from Drosophila Embryos. Jeske, M., Meyer, S., Temme, C., Freudenreich, D., Wahle, E. J. Biol. Chem. (2006) [Pubmed]
  6. Smaug recruits the CCR4/POP2/NOT deadenylase complex to trigger maternal transcript localization in the early Drosophila embryo. Semotok, J.L., Cooperstock, R.L., Pinder, B.D., Vari, H.K., Lipshitz, H.D., Smibert, C.A. Curr. Biol. (2005) [Pubmed]
  7. Smaug, a novel and conserved protein, contributes to repression of nanos mRNA translation in vitro. Smibert, C.A., Lie, Y.S., Shillinglaw, W., Henzel, W.J., Macdonald, P.M. RNA (1999) [Pubmed]
  8. Temporal complexity within a translational control element in the nanos mRNA. Forrest, K.M., Clark, I.E., Jain, R.A., Gavis, E.R. Development (2004) [Pubmed]
  9. Oskar allows nanos mRNA translation in Drosophila embryos by preventing its deadenylation by Smaug/CCR4. Zaessinger, S., Busseau, I., Simonelig, M. Development (2006) [Pubmed]
  10. Smaug, a novel RNA-binding protein that operates a translational switch in Drosophila. Dahanukar, A., Walker, J.A., Wharton, R.P. Mol. Cell (1999) [Pubmed]
  11. Crystallization and characterization of Smaug: a novel RNA-binding motif. Green, J.B., Edwards, T.A., Trincao, J., Escalante, C.R., Wharton, R.P., Aggarwal, A.K. Biochem. Biophys. Res. Commun. (2002) [Pubmed]
 
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