Structural basis for transcription complex disruption by the Mfd translocase.

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Transcription-coupled repair (TCR) is a vital DNA repair pathway.
• TCR preferentially repairs lesions blocking RNA polymerase (RNAP) elongation.
• Mfd protein mediates TCR in bacteria by interacting with stalled RNAP.

Purpose of the Study:

• To elucidate the structural mechanism of Mfd engaging and dislodging stalled RNAP.
• To understand how Mfd initiates TCR.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to visualize Mfd-RNAP complexes.
• Seven distinct Mfd-elongation complex (EC) structures were determined.
• ATP and ADP-bound states of Mfd were analyzed.

Main Results:

• Detailed structures show Mfd remodeling from a repressed state.
• Mfd hides its UvrA-interacting surface during remodeling to prevent premature NER engagement.
• Mfd alters RNAP conformation to facilitate disassembly and forms a translocation complex.

Conclusions:

• Mfd employs an elaborate mechanism to distinguish paused from stalled ECs.
• Mfd disassembles stalled ECs to initiate TCR.
• The findings provide mechanistic insights into bacterial DNA repair initiation.