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High-resolution analysis of lac transcription complexes inside cells
Biochemistry
|September 9, 1986
Summary
Primer extension analysis reveals how transcription machinery alters DNA methylation at the lac UV5 promoter in Escherichia coli. RNA polymerase binding protects some DNA bases while exposing others to methylation.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- The lac UV5 promoter is a well-characterized bacterial promoter.
- Understanding transcription initiation requires knowledge of DNA-protein interactions.
- DNA methylation patterns can be influenced by protein binding.
Purpose of the Study:
- To determine the methylation pattern of the lac UV5 promoter in vivo.
- To investigate how transcription machinery affects DNA methylation.
- To propose a model for transcription complex formation.
Main Methods:
- Primer extension analysis was used to map DNA methylation.
- Dimethyl sulfate was employed as the methylating agent.
- Experiments were conducted on growing Escherichia coli.
Main Results:
- Altered methylation patterns were observed at 15 bases when transcription machinery occupied the promoter.
- Four guanosine bases near the RNA polymerase binding site were protected from methylation.
- Eleven bases on the opposite side of the DNA helix showed increased reactivity to methylation.
Conclusions:
- RNA polymerase binding induces significant changes in DNA methylation patterns.
- DNA bending by proteins may lead to hyperreactive methylation sites.
- Transcription complexes may involve interactions with deformed and torsionally stressed DNA.