A promoter relay mechanism for sequential gene activation

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• DNA supercoiling significantly impacts gene expression, with effects varying by gene sequence and genomic context.
• Position-dependent supercoiling effects are crucial for gene activation, as observed in the Salmonella typhimurium topA mutant affecting the leuABCD operon.

Purpose of the Study:

• To investigate a novel promoter relay mechanism for sequential gene expression.
• To elucidate the role of DNA supercoiling in coordinating the expression of related genes.

Main Methods:

• Analysis of gene expression in Salmonella typhimurium topA mutant.
• Identification and characterization of promoter interactions, including pilvIH, pleuO, and pleu-500.
• Functional replacement of pleuO with the inducible tac promoter (ptac).

Main Results:

• A novel promoter relay mechanism was identified, where pilvIH activates the cryptic pleuO, which in turn activates pleu-500.
• Both cis-acting pleuO activity and trans-acting LeuO protein are essential for pleu-500 activation.
• Replacing pleuO with ptac confirmed that transcription-driven DNA supercoiling is central to this relay mechanism.

Conclusions:

• This study presents the first example of a promoter relay mechanism for coordinated gene expression.
• The findings highlight the intricate interplay between DNA supercoiling, promoter activity, and sequential gene activation.