The effect ofEscherichia coliUvr protein binding on the topology of supercoiled DNA

The effects of the binding of the E. coli UvrA and UvrB proteins on the linking number (delta L) of superhelical DNA has been measured. The effects of cofactor ATP structure on UvrAB-nucleoprotein complex formation revealed that nucleotide binding, not hydrolysis, is sufficient to locally unwind the DNA helix of both ultraviolet light-damaged as well as undamaged DNAs. The extent of this unwinding is of the same order of magnitude as the nucleotide distances of the double incision sites generated by the UvrABC endonucleolytic reaction.