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The Kinetics of Transcription Elongation

The single subunit bacteriophage T7 RNA polymerase (RNAP) catalyzes each of the stages of transcription including initiation, elongation, and termination without requiring any accessory proteins. The transition from initiation to elongation is achieved through a major refolding of the protein's N-terminal domain. The mechanism that RNAP uses for transcription initiation has been elucidated, but its mechanism of transcription elongation has not been characterized in detail. This is, in part, due to the fact that elongation is an intermediate phase of transcription that begins only after 9 to 12 nucleotides of RNA are made through promoterspecific initiation.

Minimal reaction pathway of single nucleotide incorporation during elongation.

Making use of the recent observation that T7 RNAP can assume its refolded elongation structure in the presence of a promoter-free elongation substrate, Vasanti Subramanian Anand and Smita S. Patel dissected the kinetic pathway of single nucleotide incorporation during elongation. They quantified the rate of conversion from inactive complex to the active elongation complex using an RNA/DNA duplex lacking a promoter region. They then carefully quantified the reaction steps involved in nucleotide binding and incorporation and assessed the rate of translocation. This work lays the foundation for a series of studies to examine fidelity and the effect of strand displacement on the kinetics and equilibria of each step during RNA synthesis.

FOOTNOTES

See referenced article, J. Biol. Chem. 2006, 281, 35677-35685

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