Effect of temperature and 4,6'-diamidine-2-phenylindole on restriction of supercoiled Col E1 DNA by Eco RI endonuclease.

Supercoiled Col E1 DNA is split by Eco RI endonuclease at 37 degrees C without intermediate formation of open circular DNA. Accumulation of this restriction product is observed at low temperature. The fluorescent dye, 4,6'-diamidine-2-phenylindole (DAPI) inhibits restriction by Eco RI endonuclease. This effect is due to the DAPI:DNA rather than to the DAPI:Eco RI interactions.