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Termination of Translation01:44

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The large ribosomal subunit has several important structures essential to translation. These include the peptidyl transferase center (PTC) - which is the site where the peptide bond is formed - and a large, internal, water-filled tube through which the nascent polypeptide moves. This latter structure is called the Peptide Exit Tunnel, and it begins at the PTC and spans the body of the large ribosomal subunit. During translation, as the nascent polypeptide chain is synthesized, it passes through...
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During most eukaryotic translation processes, the small 40S ribosome subunit scans an mRNA from its 5' end until it encounters the first start AUG codon. The large 60S ribosomal subunit then joins the smaller one to initiate protein synthesis. The location of the translation initiation is largely determined by the nucleotides near the start codon as there may be multiple translation initiation sites present on the mRNA.  Marilyn Kozak discovered that the sequence RCCAUGG (where R...
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Initiating translation is complex because it involves multiple molecules. Initiator tRNA, ribosomal subunits, and eukaryotic initiation factors (eIFs) are all required to assemble on the initiation codon of mRNA. This process consists of several steps that are mediated by different eIFs.
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Base complementarity between the three base pairs of mRNA codon and the tRNA anticodon is not a failsafe mechanism. Inaccuracies can range from a single mismatch to no correct base pairing at all. The free energy difference between the correct and nearly correct base pairs can be as small as 3 kcal/ mol. With complementarity being the only proofreading step, the estimated error frequency would be one wrong amino acid in every 100 amino acids incorporated. However, error frequencies observed in...
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Updated: Mar 11, 2026

Analysis of Termination of Transcription Using BrUTP-strand-specific Transcription Run-on TRO Approach
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Bases estructurales para la terminación de la traducción mediada por ArfA-RF2 en los ARNm que carecen de codones de

Paul Huter1, Claudia Müller1, Bertrand Beckert1,2

  • 1Gene Center, Department of Biochemistry and Center for integrated Protein Science Munich (CiPSM), Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany.

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|December 2, 2016
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El factor de rescate alternativo A (ArfA) rescata los ribosomas bacterianos estancados en los ARNm truncados. Este estudio revela que ArfA

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Área de la Ciencia:

  • Terminación de la traducción bacteriana
  • Mecanismos de rescate del ribosoma
  • Microscopía cryoelectrónica molecular

Sus antecedentes:

  • Las bacterias utilizan el ARNm, ArfA o ArfB para rescatar ribosomas estancados en ARNm truncados que carecen de codones de parada.
  • Estudios estructurales previos aclararon los complejos tmRNA-ribosoma y ArfB-ribosoma, pero el mecanismo de ArfA no estaba claro.

Objetivo del estudio:

  • Aclarar el mecanismo estructural por el cual ArfA reconoce los ARNm truncados y recluta el factor de liberación 2 (RF2) para el rescate de ribosomas.
  • Para determinar la estructura del ribosoma Escherichia coli 70S estancado en un ARNm truncado en complejo con ArfA y RF2.

Principales métodos:

  • Reconstrucción de cryo-electrón (cryo-EM) del ribosoma 70S estancado en un ARNm truncado con ArfA y RF2.
  • Análisis estructural de las interacciones moleculares entre ArfA, RF2 y el ribosoma.

Principales resultados:

  • El extremo C de ArfA se une al canal de entrada de ARNm de la subunidad ribosómica pequeña, lo que permite la discriminación entre ARNm truncados y de longitud completa.
  • El N-terminal de ArfA interactúa con el dominio de decodificación de RF2, facilitando el reclutamiento de RF2 al ribosoma estancado.
  • ArfA estabiliza una conformación activa de RF2, imitando la terminación canónica mediante la colocación del motivo GGQ en el centro de la peptidiltransferasa.

Conclusiones:

  • La estructura revela cómo ArfA recluta RF2 para los ribosomas estancados.
  • ArfA promueve una conformación RF2 activa, lo que permite la terminación de la traducción incluso sin un codón de parada.
  • Esto proporciona una comprensión molecular de la vía de rescate del ribosoma mediada por ArfA.