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Transcription processivity: protein-DNA interactions holding together the elongation complex
E Nudler1, E Avetissova, V Markovtsov
1Public Health Research Institute, New York, NY 10016, USA.
Science (New York, N.Y.)
|July 12, 1996
Summary
Escherichia coli RNA polymerase (RNAP) can switch DNA templates during transcription elongation. This process involves distinct RNAP-DNA interactions, including a front interaction mediated by a zinc finger, ensuring continued RNA synthesis.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Transcription elongation involves a ternary complex of RNA polymerase (RNAP), DNA, and nascent RNA.
- Understanding RNAP-DNA interactions is crucial for deciphering transcription fidelity and regulation.
Purpose of the Study:
- To investigate the mechanism of DNA template switching by elongating RNAP.
- To dissect the RNAP-DNA interactions that stabilize the elongating complex.
Main Methods:
- Utilized short DNA fragments as switching templates to study RNAP-DNA interactions.
- Employed protein-DNA crosslinking to map interaction sites.
- Investigated the role of specific RNAP subunits and motifs through mutational analysis.
Main Results:
- Demonstrated that elongating RNAP can switch DNA templates via end-to-end transposition without transcript loss.
- Identified two distinct RNAP-DNA interactions: a non-ionic front (F) interaction (7-9 bp) and an ionic rear (R) interaction.
- Mapped the F interaction to the beta' subunit's zinc finger and the R interaction to the beta subunit's catalytic domain.
- Showed that disruption of the zinc finger impairs the F interaction, leading to a salt-sensitive complex with reduced processivity.
Conclusions:
- Propose a model where trilateral contacts stabilize the core complex, while the zinc finger-mediated front interaction ensures processivity.
- Highlight the importance of specific RNAP-DNA contacts for maintaining transcription fidelity during template switching.