There is still a controversy over the mechanism of promoter DNA strand separation upon open transcription complex (RPo) formation by Escheri-chia coli RNA polymerase: is it a single or a stepwise process controlled by Mg 2+ ions and temperature? To resolve this question, the kinetics of pseudo-first-order oxidation of thymine residues by KMnO4 in the )11 +2 DNA region of RPo at thekPRpromoter was examined under single-hit conditions as a function of temperature (13–37 C) in the absence or presence of 10 mmMgCl2
