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A mutant RNA polymerase that forms unusual open promoter complexes
1Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
Summary
A mutant Escherichia coli RNA polymerase (RNAP) forms stable complexes at low temperatures. This mutant RNAP provides insights into the intermediate steps of promoter opening during transcription initiation.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Escherichia coli RNA polymerase (RNAP) is crucial for gene transcription.
- Promoter opening is a key regulatory step in transcription initiation.
- Understanding RNAP-promoter interactions is vital for controlling gene expression.
Purpose of the Study:
- To characterize a novel mutant RNAP with altered promoter binding properties.
- To investigate the mechanism of promoter opening in Escherichia coli.
- To elucidate the role of specific regions in RNAP-DNA interactions.
Main Methods:
- Site-directed mutagenesis to create the RNAP mutant.
- Electrophoretic mobility shift assays (EMSAs) to study complex formation.
- Temperature-shift experiments to analyze complex stability and isomerization.
- DNAse footprinting to determine the extent of DNA melting.
Main Results:
- The mutant RNAP forms stable open promoter complexes at -20°C.
- The initial melted region in the mutant complex is shortened, extending to position -7.
- Upon addition of substrates, the mutant RNAP undergoes temperature-dependent isomerization to a wild-type-like complex (melted region to +4).
Conclusions:
- The mutant RNAP's open complex represents an intermediate in the normal promoter-opening pathway.
- These findings support a model where promoter opening initiates upstream of the -10 element and extends downstream.
- The study provides mechanistic insights into the dynamic process of transcription initiation by RNAP.