Patent ID: 7811807

Claim:
A process for purifying plasmid DNA from a nucleic acid-containing sample comprising plasmid DNA and contaminants including RNA, which process comprises a step of contaminant removal, comprising: (a) treating the nucleic acid-containing sample to form a nucleic acid solution having a concentration of monovalent cations selected from the group consisting of sodium and potassium, which nucleic acid solution includes the RNA; (b) contacting the nucleic acid solution comprising the plasmid DNA and RNA with an ultrafiltration membrane having a molecular weight exclusion limit of at least 30 kDa and no more than 100 kDa, which ultrafiltration membrane is provided in a screen-channel ultrafiltration unit which generates turbulent sample flow, whereby turbulence is provided in the region of the ultrafiltration membrane, wherein the step of contacting includes a step of diafiltration and wherein the step of contacting and the step of diafiltering the nucleic acid solution with the ultrafiltration membrane takes place in the presence of a concentration of the monovalent cations which is at least about 0.35M but does not exceed about 2M for a time sufficient to remove substantially all RNA and form a retentate containing plasmid DNA; and (c) collecting the retentate.