Structural basis of long-range transcription-translation coupling

Area of Science:

• Molecular Biology
• Structural Biology
• Microbiology

Background:

• Coupled transcription-translation complexes (TTC-B) in *Escherichia coli* involve direct interactions between RNA polymerase (RNAP) and ribosomes.
• Transcription elongation factors like NusG and NusA bridge RNAP and ribosomes in TTC-B structures.

Purpose of the Study:

• To determine the structures of coupled transcription-translation complexes with longer mRNA spacers than those found in TTC-B.
• To characterize a new class of transcription-translation coupling complexes.

Main Methods:

• Determined structures of coupled transcription-translation complexes using cryo-electron microscopy or X-ray crystallography (specific method not detailed in abstract).
• Analyzed the spatial arrangement and interactions between RNAP, ribosome, and mRNA in the new complex.

Main Results:

• Identified a new complex, termed long-range coupled transcription-translation complex (TTC-LC).
• TTC-LC features a significant rotation and translation of RNAP relative to the ribosome, creating a gap.
• Long mRNA spacers are accommodated in TTC-LC by looping out from the inter-component gap.

Conclusions:

• TTC-LC represents a distinct mode of transcription-translation coupling, accommodating longer mRNA spacers.
• Proposed that TTC-LC serves as an intermediate in the assembly and disassembly of TTC-B.
• TTC-LC may mediate transient coupling before ribosome engagement or after ribosome stalling.