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Bases estructurales de la iniciación de la transcripción: holoenzima de la ARN polimerasa con una resolución de 4 A
Katsuhiko S Murakami1, Shoko Masuda, Seth A Darst
1The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
Science (New York, N.Y.)
|May 23, 2002
Resumen
La estructura cristalina de la ARN polimerasa (ARNP) de Thermus aquaticus revela cómo la subunidad sigma guía el ensamblaje y la función de la enzima durante la iniciación de la transcripción. Esta estructura aclara el sigma.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Biología Molecular Biología Molecular
- Biología Estructural Biología estructural.
Sus antecedentes:
- La ARN polimerasa de Thermus aquaticus (RNAP) es una enzima crucial para el inicio de la transcripción.
- La subunidad sigma dirige la especificidad del promotor y el ensamblaje de RNAP.
- Comprender la estructura del complejo iniciador es vital para descifrar la regulación de la transcripción.
Objetivo del estudio:
- Determinar la estructura cristalina de la forma inicial de la ARN polimerasa (ARNP) de Thermus aquaticus compleja con la subunidad sigma.
- Para aclarar las funciones estructurales de la enzima núcleo RNAP y la subunidad sigma en la iniciación de la transcripción.
- Comprender cómo la subunidad sigma modula la actividad de la RNAP y facilita el reconocimiento del promotor.
Principales métodos:
- Se utilizó la cristalografía de rayos X para determinar la estructura.
- La resolución de la estructura determinada fue de 4 angstroms.
- El análisis estructural se centró en las interacciones entre la enzima núcleo RNAP (alpha2betabeta'omega) y la subunidad sigma.
Principales resultados:
- La estructura cristalina de la holoenzima RNAP iniciadora se resolvió a una resolución de 4 angstroms.
- Se identificaron las características estructurales clave de las interacciones entre RNAP y las subunidades sigma.
- Los dominios carboxilo-terminales de sigma están separados espacialmente pero conectados conformacionalmente por un bucle extendido.
- Este bucle influye en el canal de sitio activo de RNAP y el canal de salida de RNA.
Conclusiones:
- La subunidad sigma juega un papel crítico en el posicionamiento y la modulación de la ARN polimerasa durante la iniciación de la transcripción.
- El bucle extendido de la subunidad sigma interactúa con el sitio activo y el canal de salida, influyendo en la unión de nucleótidos y la progresión de la transcripción de ARN.
- Se propone que el desplazamiento del bucle sigma por la transcripción avanzada de ARN cause la iniciación abortiva y la liberación de sigma.
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