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EcoSal Plus

Domain 3:

Metabolism

Selenocysteine

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  • Authors: A. Böck1, and M. Thanbichler2
  • Editor: Valley Stewart3
  • VIEW AFFILIATIONS HIDE AFFILIATIONS
    Affiliations: 1: Department of Biology I, Microbiology, University of Munich, D-80638 Munich, Germany; 2: Department of Biology I, Microbiology, University of Munich, D-80638 Munich, Germany; 3: University of California, Davis, Davis, CA
  • Received 02 October 2003 Accepted 29 December 2003 Published 12 April 2004
  • Address correspondence to A. Böck august.boeck@lrz.uni-muenchen.de
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  • Abstract:

    About 50 years ago, research on the biological function of the element selenium was initiated by the report of J. Pinsent that generation of formate dehydrogenase activity by requires the presence of both selenite and molybdate in the growth medium. In nature, selenium is predominantly associated with sulfur minerals, the Se/S ratios of which vary widely depending on the geological formation. Because of the chemical similarity between the two elements, selenium can intrude into the sulfur pathway at high Se/S ratios and can be statistically incorporated into polypeptides. The central macromolecule for the synthesis and incorporation of selenocysteine is a specialized tRNA, designated tRNA. It is the product of the (previously ) gene. tRNA fulfils a multitude of functions, which are based on its unique structural properties, compared to canonical elongator RNAs. tRNA possesses the discriminator base G73 and the identity elements of serine-specific tRNA isoacceptors. The conversion of seryl-tRNA into selenocysteyl-tRNA is catalyzed by selenocysteine synthase, the product of the gene (previously the locus, which was later shown to harbor two genes, and ). The crucial element for the regulation is a putative secondary structure at the 5′ end of the untranslated region of the selAB mRNA. The generation and analysis of transcriptional and translational reporter gene fusions of and yield an expression pattern identical to that obtained by measuring the actual amounts of SelA and SelB proteins.

  • Citation: Böck A, Thanbichler M. 2004. Selenocysteine, EcoSal Plus 2004; doi:10.1128/ecosalplus.3.6.1.1

Key Concept Ranking

Nuclear Magnetic Resonance Spectroscopy
0.44226918
Elongation Factor Tu
0.33797252
Amino Acids
0.31473985
0.44226918

References

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2004-04-12
2017-11-23

Abstract:

About 50 years ago, research on the biological function of the element selenium was initiated by the report of J. Pinsent that generation of formate dehydrogenase activity by requires the presence of both selenite and molybdate in the growth medium. In nature, selenium is predominantly associated with sulfur minerals, the Se/S ratios of which vary widely depending on the geological formation. Because of the chemical similarity between the two elements, selenium can intrude into the sulfur pathway at high Se/S ratios and can be statistically incorporated into polypeptides. The central macromolecule for the synthesis and incorporation of selenocysteine is a specialized tRNA, designated tRNA. It is the product of the (previously ) gene. tRNA fulfils a multitude of functions, which are based on its unique structural properties, compared to canonical elongator RNAs. tRNA possesses the discriminator base G73 and the identity elements of serine-specific tRNA isoacceptors. The conversion of seryl-tRNA into selenocysteyl-tRNA is catalyzed by selenocysteine synthase, the product of the gene (previously the locus, which was later shown to harbor two genes, and ). The crucial element for the regulation is a putative secondary structure at the 5′ end of the untranslated region of the selAB mRNA. The generation and analysis of transcriptional and translational reporter gene fusions of and yield an expression pattern identical to that obtained by measuring the actual amounts of SelA and SelB proteins.

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Figures

Image of Figure 1
Figure 1

The specific reactions are indicated in boldface. mnm S U, 5-methylaminomethyl-2-thio-uridine; mnm Se U, 5-methylaminomethyl-2-seleno-uridine.

Citation: Böck A, Thanbichler M. 2004. Selenocysteine, EcoSal Plus 2004; doi:10.1128/ecosalplus.3.6.1.1
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Image of Figure 2
Figure 2

Elements involved in recognition by seryl-tRNA synthetase in canonical tRNA are shaded; antiderminants against recognition by EF-Tu are hatched. The modified bases are dihydrouridine (D), pseudouridine (ψ), isopentenyladenosine (i A), and ribothymidine (T). Tertiary interactions involving base pairing are indicated by lines; those mediated by intercalation are shown by arrows.

Citation: Böck A, Thanbichler M. 2004. Selenocysteine, EcoSal Plus 2004; doi:10.1128/ecosalplus.3.6.1.1
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Image of Figure 3
Figure 3

SerS, seryl-tRNA synthetase; SS, selenocysteine synthase; SelD, selenophosphate synthetase.

Citation: Böck A, Thanbichler M. 2004. Selenocysteine, EcoSal Plus 2004; doi:10.1128/ecosalplus.3.6.1.1
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Image of Figure 4
Figure 4

G1 to G5 indicate the motifs involved in the binding of guanosine nucleotides. The Roman numerals above the scheme indicate the domains of the two proteins ( ). The characteristic deletions present in SelB are indicated below the sequence scheme. (B) Organization of the operon. P, promoter. (C) Comparison of the sequences of the and SECIS elements with the SECIS-like motif in the 5′ untranslated region of the operon.

Citation: Böck A, Thanbichler M. 2004. Selenocysteine, EcoSal Plus 2004; doi:10.1128/ecosalplus.3.6.1.1
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Image of Figure 5
Figure 5

Without the quaternary complex assembled at the SECIS-like element (state A), translation of and is derepressed. Biosynthesis of Sec-tRNA (a), which is dependent on a sufficient supply of selenide, allows the formation of the regulatory complex on the 5′ mRNA structure of the transcript (c), thereby decreasing the rate of translation of and, to a lesser extent, (state B). Competition between the SECIS-like element and the SECIS element of selenoprotein mRNAs (d) leads to the dissociation of the regulatory complex and to the formation of the SelB-GTP-Sec–tRNA-SECIS complex (b), which catalyzes the decoding of UGA as selenocysteine. After A-site interaction and translocation of the ribosome (e), SelB and tRNA are released and ready to reenter the cycle.

Citation: Böck A, Thanbichler M. 2004. Selenocysteine, EcoSal Plus 2004; doi:10.1128/ecosalplus.3.6.1.1
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