Nuclease-induced DNA structural changes assessed by flow cytometry with the intercalating dye propidium iodide

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Nucleases are enzymes that cleave DNA.
• DNA structure and conformation influence its accessibility to dyes.
• Flow cytometry is a technique used to analyze DNA content and structure.

Purpose of the Study:

• To investigate DNA structural changes induced by various nucleases.
• To assess the impact of nuclease activity on DNA stainability with fluorescent dyes.
• To differentiate between conformation-specific and sequence-specific nuclease effects on DNA.

Main Methods:

• Flow cytometry was used to analyze isolated HeLa nuclei.
• Nuclei were digested with different nucleases: DNAse I, micrococcal nuclease, S1 nuclease, Neurospora crassa nuclease, Eco RI, Alu I, and Not I.
• Changes in DNA stainability were assessed using propidium iodide (PI) and Hoechst 33258, with mithramycin as a control.

Main Results:

• Mild digestion with DNAse I, micrococcal nuclease, S1, and N. crassa nucleases increased PI fluorescence intensity by 15-30%.
• Restriction enzymes (Eco RI, Alu I, Not I) did not significantly alter fluorescence.
• DNAse I-induced changes were observed with Hoechst 33258 but not mithramycin, indicating a conformational effect.
• PI fluorescence changes were dye concentration-dependent, mimicking relaxed vs. supercoiled DNA behavior.

Conclusions:

• Conformation-specific nucleases, not sequence-specific ones, induce DNA relaxation.
• DNA structural relaxation increases accessibility to intercalating dyes like PI.
• Flow cytometry can detect nuclease-induced DNA conformational changes.