My palsmid is around 9000 bp in pSectag2-MycHis-IRES-EGFP vector with ampicillin resistance and use DH-alpha E.coli.. It is highcopy plasmid. I tried both large and small volume of culture medium. When i do mini prep to confirm the plasmid using 2 ml of culture from large culture (200ml to 500ml), i get quite good amount of plasmid for example 0.8 to 1.0 ug/ul eluted with 10 to 20 ul TE). But after conformation, when I do Max-prep the plasmid yield is very low for example 0.2 ug/ul to 0.5 ug/ul eluted with 100 ul TE 300-500ml culture media. One year ago i faced the same problem. i used several reagent from different company but did not get any solution but finally it was solved by some of my personal tricks but now all of my tricks are failed and i am getting crazy about this.
How did you overcome finally for that problem? can you give me some suggestion?