Structural basis of ECF-σ-factor-dependent transcription initiation.

Area of Science:

• Molecular Biology
• Structural Biology
• Microbiology

Background:

• Extracytoplasmic (ECF) σ factors are a major class of alternative σ factors.
• They share similarities with primary σ factors but possess simpler structures, containing only conserved regions 2 (σR2) and 4 (σR4).

Purpose of the Study:

• To elucidate the structural basis of transcription initiation complexes involving ECF σ factors.

Main Methods:

• Crystal structure determination of transcription initiation complexes.
• Complexes included Mycobacterium tuberculosis RNA polymerase (RNAP), ECF σ factor σ^L, and promoter DNA.

Main Results:

• ECF σ factor regions σR2 and σR4 bind to RNAP at conserved sites, similar to primary σ factors.
• The connector region of the ECF σ factor, though sequence-divergent, follows the same path within RNAP as in primary σ factors.
• ECF σ factors employ a conserved strategy for promoter DNA binding and unwinding.

Conclusions:

• The study defines key protein-protein and protein-DNA interactions in ECF σ-factor-dependent transcription initiation.
• This provides a structural foundation for understanding alternative sigma factor function in bacteria.