Supercoiling Induced by Transcription
The biological implications of supercoiling by transcription are potentially significant (Pruss and Drlica 1989; Lilley and Higgins 1991), and a fundamental question is the extent to which transcription determines the level of DNA supercoiling in vivo. Transcription can induce supercoiling of the template by virtue of the topological relationship between DNA and elongating RNA polymerase (Liu and Wang 1987). In some models, transcription elongation requires that polymerase follows the helical screw of the DNA such that there one 360° rotation between the enzyme and DNA for each 10.5 bp transcribed (Gamper and Hearst 1982). Since RNA polymerase elongates at the rate of about 40 nucleotides/s, an efficiently anchored transcription complex should introduce approximately four negative super-turns upstream and four positive superturns downstream from an actively expressed gene each second. This would suggest extraordinarily fast rates of localized supercoiling after the onset of transcription. The goal of this chapter is to summarize and examine our understanding of the kinetics and mechanisms of supercoiling induced by transcription and to relate these insights to the mechanics of transcription elongation.
KeywordsMigration Torque Codon Polypeptide Posit
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