Intercalator effects on DNA loop extrusion by SMC proteins

Intercalating dyes reduce SMC loop-extrusion rates by about two-fold, with dye-free Saccharomyces cerevisiae condensin extruding at 1.75{+/-}0.26 kb/s.

• Why it matters: Fluorescent intercalators are commonly used in single-molecule DNA assays, but their quantitative effects on DNA-processing proteins like SMC complexes are not fully characterized.
• What they did: The study visualized extruded loops using dye fluorescence, systematically testing four intercalators and measuring SMC binding and ATPase activity, plus a new dye-free local-spot assay.
• The result: Loop extrusion was qualitatively not affected, but quantitative parameters changed: intercalators stiffened DNA and reduced SMC binding/ATPase activity, yielding a two-fold lower extrusion rate than dye-free conditions.