The supercoil-stabilised cruciform of ColE1 is hyper-reactive to osmium tetroxide.

摘要: Supercoiled pColIR215 contains a site of pronounced hyper-reactivity towards modification by osmium tetroxide, reagent known to be single-strand-selective. The hypersensitivity has been mapped the ColE1 inverted repeat, believed extrude cruciform in supercoiled DNA. Linear or relaxed plasmids are not modified reagent. We conclude that formation is responsible for site-selective modification. Fine mapping as function time revealed initial reaction occurs at centre i.e., unpaired loop cruciform, but region rapidly expands outwards from this point.