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DNA replication is initiated at sites containing predefined DNA sequences known as origins of replication. DNA is unwound at these sites by the minichromosome maintenance (MCM) helicase and other factors such as Cdc45 and the associated GINS complex.The unwound single strands are protected by replication protein A (RPA) until DNA polymerase starts synthesizing DNA at the 5’ end of the strand in the same direction as the replication fork. To prevent the replication fork from falling apart,...
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El volcado de nucleosomas impulsa la corrección cinética y la procesividad por SWR1

Paul Girvan1,2, Adam S B Jalal1, Elizabeth A McCormack1

  • 1Section of Structural Biology, Department of Infectious Disease, Faculty of Medicine, Imperial College London, London, UK.

Nature
|November 7, 2024
PubMed
Resumen

El complejo SWR1 facilita el intercambio de dímeros de histona en los nucleosomas de la levadura. Este estudio revela un mecanismo de dos pasos en el que los nucleosomas se invierten, lo que permite un intercambio doble eficiente sin disociación.

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Área de la Ciencia:

  • Biología de la cromatina
  • Mecanismos moleculares de reparación y replicación del ADN
  • La epigenética

Sus antecedentes:

  • El complejo SWR1 es crucial para reemplazar las histonas canónicas H2A-H2B por las Htz1-H2B en los nucleosomas.
  • Comprender el mecanismo de intercambio mediado por SWR1 es clave para comprender la dinámica del nucleosoma y la regulación epigenética.

Objetivo del estudio:

  • Elucidar el mecanismo paso a paso del intercambio de doble dímero de histona por el complejo SWR1.
  • Investigar si se requiere la liberación de nucleosomas para el intercambio doble procesal.
  • Determinar el papel de la inversión de nucleosomas y la subunidad Swc2 en la función del complejo SWR1.

Principales métodos:

  • Análisis de una sola molécula para observar el intercambio de dimeros de histona en tiempo real.
  • Microscopía criolectrónica para visualizar los intermedios estructurales y los estados conformacionales.
  • Ensayos bioquímicos para medir los tiempos de permanencia de la unión y los intermedios de reacción.

Principales resultados:

  • Demostró un mecanismo de intercambio doble en dos pasos para los dímeros H2A-H2B por SWR1, que ocurre sin liberación de nucleosomas.
  • Se observa que los nucleosomas cambian entre estados distintos, presentando diferentes caras y dímeros de histona a SWR1.
  • Identificó un hexasoma intermedio unido en una orientación fija y destacó el papel de la subunidad Swc2 en facilitar los cambios conformacionales.

Conclusiones:

  • El complejo SWR1 emplea un mecanismo procesativo para el intercambio de dímeros dobles, que involucra la inversión de nucleosomas e interacciones específicas de subunidades.
  • Este mecanismo permite a SWR1 "corregir" de manera eficiente las identidades de los dímeros de histona dentro de los nucleosomas.
  • Los hallazgos proporcionan una comprensión molecular detallada del papel de SWR1 en la remodelación de la cromatina y la regulación epigenética.