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Arquitectura de un complejo de preiniciación de la transcripción de la ARN polimerasa II
Kenji Murakami1, Hans Elmlund, Nir Kalisman
1Department of Structural Biology, Stanford University, Stanford, CA 94305, USA.
Science (New York, N.Y.)
|September 28, 2013
Resumen
Los investigadores mapearon el complejo de preiniciación de la transcripción de la ARN polimerasa II (PIC). La estructura revela que el ADN promotor interactúa con los factores de transcripción, situados por encima de la ARN polimerasa II para la entrada en el ADN.
Área de la Ciencia:
- Biología Molecular Biología Molecular
- Biología Estructural Biología Estructural
- La bioquímica es la bioquímica.
Sus antecedentes:
- La ARN polimerasa II (pol II) es central para la transcripción génica.
- El complejo de preiniciación (PIC) se ensambla en los promotores de genes antes de que comience la transcripción.
- Comprender la estructura del PIC es crucial para descifrar la regulación de la transcripción.
Objetivo del estudio:
- Determinar la estructura de alta resolución del complejo de preiniciación de transcripción (PIC) completo de 32 proteínas de ARN polimerasa II.
- Para aclarar la disposición espacial de los factores generales de transcripción (GTF) y pol II dentro del PIC.
- Para entender cómo el PIC está preparado para la iniciación de la transcripción.
Principales métodos:
- Se empleó microscopía electrónica criogénica (cryo-EM) para visualizar el PIC.
- Se utilizó el enlace cruzado químico junto con la espectrometría de masas (XL-MS) para mapear las interacciones de las subunidades.
- El análisis estructural integrador combinó estos conjuntos de datos.
Principales resultados:
- El PIC de 32 proteínas exhibió una organización bipartidista distinta, separando los GTF y el pol II.
- Se encontró que el ADN promotor estaba asociado exclusivamente con los GTF, colocados por encima de la hendidura del sitio activo pol II.
- El ADN no entró directamente en contacto con pol II en el estado previo a la iniciación.
Conclusiones:
- La estructura PIC determinada revela un estado equilibrado para la iniciación de la transcripción.
- La disposición estructural facilita la transición a una burbuja de transcripción activa.
- Esto posiciona el ADN para entrar en la hendidura pol II, un paso clave en la transcripción.
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