Repression by binding of H-NS within the transcription unit

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• The nucleoid-associated protein H-NS is known to repress transcription by forming complexes near promoters.
• Investigating H-NS repression mechanisms within transcription units provides insight into gene regulation.

Purpose of the Study:

• To investigate the role of H-NS binding within transcription units, specifically the bgl and proU operons.
• To determine the mechanism by which H-NS binding within the transcription unit inhibits transcription initiation.

Main Methods:

• Analysis of bgl and proU reporter constructs.
• Determination of RNA polymerase occupancy within the bgl transcription unit.
• Chloroacetaldehyde footprinting of RNA polymerase promoter complexes.

Main Results:

• H-NS repression of bgl and proU requires both upstream regulatory elements (URE) and downstream regulatory elements (DRE).
• H-NS binding to the bgl-DRE inhibits transcription initiation before open complex formation, similar to proU.
• RNA polymerase is poised at the proU promoter under low osmolarity, with reduced poising and H-NS repression at high osmolarity.
• H-NS repression via URE and DRE is synergistic and inversely correlates with promoter activity.

Conclusions:

• H-NS can repress transcription by binding within the transcription unit, mediated by DREs.
• The mechanism involves inhibition of transcription initiation before open complex formation.
• Promoter strength influences the efficiency of H-NS repression via DREs.