Thermodynamics of the ColE1 cruciform

摘要: Abstract The sensitivity of the ColE1 cruciform to four enzyme and chemical probes secondary structure has been studied as a function plasmid topology. Purified topoisomers pColIR515 have probed with S1 nuclease, Bal31 phage T4 endonuclease VII or osmium tetroxide, site-specific reaction quantified. Closely similar profiles reactivity linking difference were obtained for each probe. Electrophoresis pure on polyacrylamide/agarose gels revealed discontinuity in migration difference. Above threshold difference, exhibit pronounced reduction mobility. at which this band shift is found correlates precisely that required probes. We conclude both probing topological methods are valuable study supercoiled DNA. measured accuracy allow calculation twist change accompanies transition, corresponding ΔTw = −3.2 ± 0.1. Using value together critical we calculate free energy formation ΔG 18.4 0.5 kcal mol− (1 4.184 kJ).