Molecular Biology of the Gene 7th Edition by Richard Losick, James Watson, Michael Levine, Tamara Baker, Alexander Gann

Exercise 7

You isolated a 10,500-bp plasmid (supercoiled, cccDNA) from E. coli. The plasmid contains one unique recognition site for EcoRI, a restriction enzyme. Restriction enzymes recognize a specific sequence and cut both strands of the DNA at that sequence (Chapter 21). You briefly incubated the cccDNA at 37°C in four separate reactions containing the components listed below. You ran the reaction on an agarose gel and visualized the DNA using ethidium bromide and UV light. The reactions included the appropriate buffer and ATP when required. An agarose gel containing four lanes of possible products is given below. For each reaction, indicate which lane on the gel contains the products that you would expect to see on your agarose gel.

i. Buffer alone
ii. DNase I (brief treatment)
iii. Topoisomerase I
iv. EcoRI