The distribution of plasmid topoisomers and the presence of impurities likeRNA, gDNA, and residual proteins in the final pDNA were alsoinvestigated (Table 2 and Fig. 3).
An agarose gel electrophoresis analysis with ethidium bromide staining showed that RNA impurities were absent and that supercoiled isoforms predominate inthe three pDNA preparations (Fig. 3).
The levels of protein contamination were residual and independent of the starting cells.
Although low amounts of gDNA were detected in samples iso-lated from GALG20 and MG1655endArecA cells, gDNA contentin pDNA preparations derived from DH5 was higher than the rec-ommended value (