NewMethodforLarge-Scale Preparation ofCovalently Closed XDNA Molecules

The former procedure necessi-tates the purification of the enzyme and, inaddition, results in moleculesofvaryingdegreesof superhelicity depending uponthe conditionsemployedin the reaction mixture (3); the prod-uct, therefore, is not necessarily the same asthat occurring in vivo. The yield of covalentlyclosed circles formed in vivo by superinfection,on the other