Virologica Sinica

, Volume 28, Issue 6, pp 337–344 | Cite as

Snapshots of a viral RNA polymerase switching gears from transcription initiation to elongation

  • Karsten Theis


During transcription initiation, RNA polymerase binds tightly to the promoter DNA defining the start of transcription, transcribes comparatively slowly, and frequently releases short transcripts (3–8 nucleotides) in a process called abortive cycling. Transitioning to elongation, the second phase of transcription, the polymerase dissociates from the promoter while RNA synthesis continues. Elongation is characterized by higher rates of transcription and tight binding to the RNA transcript. The RNA polymerase from enterophage T7 (T7 RNAP) has been used as a model to understand the mechanism of transcription in general, and the transition from initiation to elongation specifically. This single-subunit enzyme undergoes dramatic conformational changes during this transition to support the changing requirements of nucleic acid interactions while continuously maintaining polymerase function. Crystal structures, available of multiple stages of the initiation complex and of the elongation complex, combined with biochemical and biophysical data, offer molecular detail of the transition. Some of the crystal structures contain a variant of T7 RNAP where proline 266 is substituted by leucine. This variant shows less abortive products and altered timing of transition, and is a valuable tool to study these processes. The structural transitions from early to late initiation are well understood and are consistent with solution data. The timing of events and the structural intermediates in the transition from late initiation to elongation are less well understood, but the available data allows one to formulate testable models of the transition to guide further research.


RNA polymerase Transcription Elongation Crystal structure 


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Copyright information

© Wuhan Institute of Virology, CAS and Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Department of Chemical and Physical SciencesWestfield State UniversityWestfieldUSA

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