distinguishing circular and linear DNA

[cmgross]

I need to learn at least 2 different ways to determine if a 100 kb ds DNA viral genome is circular or linear. We are starting with highly purified viral DNA in a tube. I know that circular and linear DNA run differently on a gel, but I don't think you can run fragments that big on an agarose gel. Thanks

[canalon]

Pulse field gel electrophoresis (PFGE) is your friend

[JackBean]

By restriction enzymes you could recognise it (circular = you will get as many fragments, as many times you cut; linear = you get +1 fragment), but I guess ou don't have restriction map, do you?

[qqsvery]

U can try density gradient centrifugation method！good luck！