Molecular Biology

First Step to Commitment

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Science  29 Sep 2000:
Vol. 289, Issue 5488, pp. 2243
DOI: 10.1126/science.289.5488.2243a

In eukaryotic transcription, a molecular machine consisting of RNA polymerase II together with a set of basal transcription factors acts at all promoters. The factors TFIIE and TFIIH are involved in facilitating transitions from a preinitiation complex to an open complex that links together the first few ribonucleotides and then to a stable elongation complex (containing a 15-nucleotide RNA) that allows subsequent synthesis of the full length transcript. But what happens to RNA polymerase II itself during these transitions?

Kugel and Goodrich have used a minimal in vitro transcription system, which does not require TFIIE or TFIIH, to measure rate constants for discrete steps of single rounds of transcription. They find that a transition occurs after initiation that commits RNA polymerase II to releasing the promoter and forming the elongation complex. This transition, termed escape commitment, is rapid and is complete after synthesis of the first four nucleotides of the transcript; TFIIH serves to enhance escape commitment. The authors present a kinetic model for transcription that comprises five steps: preinitiation complex formation, initiation, escape commitment, promoter escape, and transcript elongation. — VV

J. Biol. Chem., in press.

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