Structural, functional, and genetic analyses of the actinobacterial transcription factor RbpA

Area of Science:

• Molecular biology
• Microbiology
• Structural biology

Background:

• Gene expression regulation is crucial, with transcription initiation being a key control point.
• Transcription activators like RbpA are essential for this process, particularly in Mycobacterium tuberculosis (Mtb).
• RbpA exhibits selective binding to specific sigma (σ)-factors.

Purpose of the Study:

• To elucidate the molecular mechanism of RbpA's function as a transcription activator.
• To determine the structural basis for RbpA's σ-factor selectivity.
• To investigate RbpA's interaction with promoter DNA during transcription initiation.

Main Methods:

• X-ray crystallography to determine the structure of Mtb RbpA-SID bound to σ(A) domain 2.
• Site-directed mutagenesis and functional assays to confirm interactions and selectivity.
• In vivo and in vitro studies to support DNA binding models.

Main Results:

• The Mtb RbpA σ-interacting domain (SID) and basic linker are sufficient for transcription activation.
• The crystal structure reveals RbpA interacts with conserved and the unique nonconserved region (NCR) of σ(A).
• Structural modeling and experimental data suggest RbpA also contacts promoter DNA.

Conclusions:

• The study provides the first structural evidence of a protein interacting with the σ-factor NCR.
• RbpA's interaction with both σ(A) and promoter DNA is key to its function as a transcription activator.
• This work enhances the understanding of transcription regulation mechanisms in actinobacteria.