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La estructura de una polimerasa de ARN T7 transcriptor en transición desde la iniciación a la elongación
Kimberly J Durniak1, Scott Bailey, Thomas A Steitz
1Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT 06520-8114, USA.
Science (New York, N.Y.)
|October 25, 2008
Resumen
Los estudios estructurales revelan cómo las transiciones de la ARN polimerasa dependiente del ADN de los bacteriófagos T7 (T7 RNAP) entre la iniciación y el alargamiento de la transcripción. Las estructuras cristalinas intermedias muestran la rotación del dominio de unión al promotor, manteniendo el contacto con el ADN al tiempo que acomodan la síntesis de ARN.
Área de la Ciencia:
- Biología Molecular Biología Molecular
- Biología Estructural Biología estructural.
- La bioquímica es la bioquímica.
Sus antecedentes:
- La polimerasa de ARN dependiente del ADN de los bacteriófagos T7 (T7 RNAP) sufre cambios conformacionales significativos entre el inicio de la transcripción y el alargamiento.
- El mecanismo preciso de esta transición, en particular la que involucra el dominio amino-terminal, sigue siendo incompletamente entendido.
Objetivo del estudio:
- Para aclarar los estados estructurales intermedios de T7 RNAP durante la transición de la iniciación de la transcripción a la elongación.
- Proporcionar conocimientos estructurales de alta resolución sobre la dinámica conformacional del ARNAP T7.
Principales métodos:
- Se empleó cristalografía de rayos X para determinar las estructuras de T7 RNAP.
- Se analizaron complejos de ARNAP T7 con ADN promotor y transcripciones cortas de ARN (7 y 8 nucleótidos).
Principales resultados:
- Las estructuras cristalinas revelaron estados intermedios de T7 RNAP durante la transcripción.
- El dominio de unión al promotor (PBD) y el promotor unido giran ~45 grados tras la síntesis de una transcripción de ARN de 8 nucleótidos.
- Esta rotación mantiene los contactos del promotor y expande el sitio activo para el creciente heterodúplex ARN-ADN.
Conclusiones:
- Los cambios estructurales observados iluminan la vía de T7 RNAP desde la iniciación hasta la elongación.
- La rotación del PBD es un mecanismo clave para acomodar la transición mientras se preservan las interacciones esenciales del ADN.
- El subdominio H permanece en una posición similar a la iniciación, lo que indica una transición no uniforme del dominio amino-terminal.
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