A method for improving the replication of a covalently closed circular
plasmid is provided. The method includes providing a covalently closed circular
plasmid having a Pol I-dependent
origin of replication, and an insert including a structured
DNA sequence selected from
inverted repeat sequences,
direct repeat sequences, homopolymeric repeat sequences, eukaryotic origins of replication or eukaryotic
promoter enhancer sequences, wherein the structured
DNA sequence is located at a distance of less than 1000 bp from the Pol I-dependent
origin of replication in the direction of replication. The method also includes modifying the covalently closed circular recombinant molecule such that the Pol I-dependent
origin of replication is replaced with a Pol III-dependent origin of replication, whereby the
resultant Pol III-dependent origin of replication covalently closed circular
plasmid has improved replication. An antibiotic
marker free covalently closed circular
recombinant DNA molecule is also provided.