A number of differences were observed among the three strainsin terms of process yield and quality of final product (Table 2). AnHPLC analysis showed that clarified lysates obtained from GALG20cells had the highest percentage of pDNA (41% vs 31% and 26%for MG1655endArecA and DH5, respectively). The distribu-tion 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 electrophoresisanalysis with ethidium bromide staining showed that RNA impu-rities were absent and that supercoiled isoforms predominate inthe three pDNA preparations (Fig. 3). The levels of protein con-tamination 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 (