Plasmid appears as two bands after double digestion - (Dec/12/2005 )

i have recently performed a double restriction digestion. The undigested pUC18 recombinant plasmid appeared as two bands on the agarose gel. Why are there two bands since the recombinant was not digested? Shouldn't there technically just be one band?

Uncut Plasmid DNA runs as supercoiled (faster), Linear, and nicked DNA. Check details here
Under the topic:" Migration of DNA Fragments in Agarose"

If ur plasmid has restriction sites for both the enzymes(u had used two enzymes for digestion0 u'll
get two bands ...why cant u check the restriction sites of ur plasmid using Neb cutter available at www.neb.com

ravella