期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 101, 期 14, 页码 4776-4780出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0307241101
关键词
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资金
- NIGMS NIH HHS [R01 GM041376, R37 GM041376, GM41376] Funding Source: Medline
By monitoring the end-to-end extension of a mechanically stretched, supercoiled, single DNA molecule, we have been able directly to observe the change in extension associated with unwinding of approximately one turn of promoter DNA by RNA polymerase (RNAP). By performing parallel experiments with negatively and positively supercoiled DNA, we have been able to deconvolute the change in extension caused by RNAP-dependent DNA unwinding (with approximate to1-bp resolution) and the change in extension caused by RNAP-dependent DNA compaction (with approximate to5-nm resolution). We have used this approach to quantify the extent of unwinding and compaction, the kinetics of unwinding and compaction, and effects of supercoiling, sequence, ppGpp, and nucleotides. We also have used this approach to detect promoter clearance and promoter recycling by successive RNAP molecules. We find that the rate of formation and the stability of the unwound complex depend profoundly on supercoiling and that supercoiling exerts its effects mechanically (through torque), and not structurally (through the number and position of supercoils). The approach should permit analysis of other nucleic-acid-processing factors that cause changes in DNA twist and/or DNA compaction.
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