A wider application of minicircle (MC) vectors in gene therapy research depends critically on the ability to purify supercoiled (sc) MC from related miniplasmid (MP) and parental plasmid (PP) impurities. This protocol describes a purification strategy that combines the in vitro enzymatic relaxation of sc MP and PP impurities by a nicking endonuclease, and topoisomer separation and RNA clearance by hydrophobic interaction chromatography. The time required to follow the full protocol, from production to isolation of sc MC, is approximately 50 h. The process delivers sc MCs that are virtually free from MP, PP, RNA, and protein impurities.
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