The study of DNA-RNA-polymerase complexes by kinetic formaldehyde method

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Understanding DNA-enzyme interactions is crucial for gene regulation.
• Detecting structural changes in DNA during protein binding is challenging.
• RNA polymerase (RNAP) binding to DNA initiates transcription.

Purpose of the Study:

• To develop and calibrate a modified kinetic formaldehyde method for detecting DNA defects.
• To investigate the impact of RNA polymerase binding on DNA structure.
• To elucidate the mechanism of DNA defect formation upon RNAP interaction.

Main Methods:

• Modification of the kinetic formaldehyde method for DNA defect detection.
• Preincubation of DNA with RNA polymerase in the absence of nucleoside triphosphates.
• Fixation of DNA-enzyme complexes using varying formaldehyde concentrations and times.
• Analysis of DNA defect formation under different ionic strengths and temperatures.

Main Results:

• The modified method reliably detects locally denatured regions (defects) in DNA.
• DNA defect formation is constant within formaldehyde fixation concentrations (0.05%-0.5%) and times (2-100 min).
• The number of defects plateaus with increasing RNA polymerase concentration, indicating monomeric binding.
• Approximately 400-500 nucleotide pairs separate defects at enzyme excess.
• Increased ionic strength and temperatures above 20°C reduce DNA defects, with saturation above 30°C.
• A sharp transition in defect formation occurs between 20°C and 30°C.

Conclusions:

• RNA polymerase binding induces DNA unwinding or weakening, creating detectable defects.
• The formation of these defects is temperature-dependent, with a critical transition range.
• The findings suggest a mechanism for DNA structural changes preceding transcription initiation.