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Two open complexes and a requirement for Mg2+ to open the lambda PR transcription start site
1Department of Chemistry, University of Wisconsin, Madison 53706.
Science (New York, N.Y.)
|January 15, 1993
Summary
Magnesium ions (Mg2+) alter the structure of Escherichia coli RNA polymerase open complexes at the lambda PR promoter. This structural change is essential for forming the transcription-competent open complex RPo2.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Escherichia coli RNA polymerase (Eσ70) forms different open complexes at promoter sites.
- Magnesium ions (Mg2+) are known to influence transcription initiation.
- Previous kinetic studies suggested Mg2+ uptake is required for RPo2 formation.
Purpose of the Study:
- To investigate the structural differences between RNA polymerase open complexes formed with and without Mg2+.
- To elucidate the role of Mg2+ in the transition from RPo1 to RPo2 at the lambda PR promoter.
Main Methods:
- Potassium permanganate (KMnO4) footprinting was employed.
- Experiments were conducted in the absence and presence of Mg2+.
- Analysis focused on the lambda PR promoter and Eσ70 RNA polymerase.
Main Results:
- Two distinct open complexes, RPo1 (without Mg2+) and RPo2 (with Mg2+), were identified.
- RP01 exhibited a single-stranded region of at most 12 bases.
- RP02 displayed a larger single-stranded region, spanning at least 14 bases and extending to the transcription start site (+1, +2).
Conclusions:
- The presence of Mg2+ induces significant structural changes in the RNA polymerase open complex.
- These structural alterations, particularly the extended single-stranded region in RPo2, provide a structural basis for the necessity of Mg2+ uptake in forming the transcriptionally active RPo2 complex.