Structural principles of transcriptional collisions.

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• RNA polymerase (RNAP) transcribes DNA, but faces obstacles like DNA-bound proteins and other RNAPs.
• The mechanisms by which RNAP overcomes these transcription-impeding roadblocks are not fully understood.

Purpose of the Study:

• To visualize the structural dynamics of *E. coli* RNAP during collisions with roadblocks.
• To elucidate the mechanisms by which RNAP navigates and overcomes transcription conflicts.

Main Methods:

• Cryo-electron microscopy was used to capture structures of actively transcribing RNAP.
• RNAP collisions were studied using an inactivated restriction enzyme (EcoRI*) and converging RNAPs.

Main Results:

• Collisions induce RNAP backtracking into a swiveled, inactive state, coupled with DNA deformation.
• This swiveling mechanism stabilizes RNAP pausing across various collision geometries.
• RNAP-RNAP collisions show heterogeneity, influenced by nascent transcript structures and termination sites.

Conclusions:

• A structural framework for RNAP collision mechanics was established.
• RNAP swiveling and backtracking rescue are key factors in roadblock bypass.
• Understanding these dynamics is crucial for robust gene expression.