Question: An unknown enzyme that affects DNA has been isolated from E. coli. When a solution of this enzyme is mixed with supercoiled plasmid DNA, its only effect is to relax DNA. At the end of the exposure to the enzyme solution, the plasmid DNA is covalently closed and is still circular. This enzyme is one: 
 Options:  <1> Restriction endonuclease. <2> Primasa <3> Reverse transcriptase <4> Helicasa <5> Topoisomerase
5