DNA twist as a transcriptional sensor for environmental changes

Area of Science:

• Molecular Biology
• Genetics
• Biophysics

Background:

• Environmental shifts induce changes in bacterial plasmid DNA linking number, often attributed to altered superhelical density.
• Superhelical density is known to influence DNA transcription in vitro, suggesting a role in gene expression control.

Purpose of the Study:

• To investigate whether changes in DNA twist, rather than superhelical density, explain observed linking number variations.
• To explore the role of DNA twist in regulating gene expression, particularly sigma 70 promoters.

Main Methods:

• Analysis of the relationship between linking number (Lk), twist (Tw), and writhe (Wr) using the equation delta Lk = delta Tw + delta Wr.
• Review of published data on promoter activity variations in response to linking number changes.
• Examination of the Menzel and Gellert homeostatic model for DNA superhelical density regulation.

Main Results:

• Demonstrated that under homeostatic regulation of superhelical density, changes in linking number (delta Lk) primarily reflect changes in DNA twist (delta Tw).
• Identified published studies where promoter activity variations correlate with linking number changes that can be explained by twist alterations.
• Proposed that DNA twist influences the relative orientation of promoter regions (-35 and -10 elements).

Conclusions:

• Environmental factors influencing DNA helical pitch can alter DNA twist, thereby affecting gene expression.
• Certain sigma 70 promoters are highly sensitive to the spatial arrangement of -35 and -10 regions, which is modulated by DNA twist.
• DNA twist, influenced by environmental conditions, serves as a critical regulatory mechanism for gene expression in bacteria.