[Reaction of endonuclease EcoRI with DNA of the plasmid ColEI]

Interaction of restrictase EcoRI with supercoiled and open forms of ColEI DNA is studied in the range 0-55 degrees. At temperatures 25-37 degrees superhelical ColEI DNA is converted to linear form, the most complete cleavage of supercoiled molecules were observed at 25 degrees. This reaction is not followed by accumulation of intermediate open circular DNA forms. At 45-55 degrees open circular DNA forms with nicks at the restriction site are formed along with linear molecules. Similar effects were observed at 10 degrees, whereas at 0 degree only open circular DNA molecules are formed.