Large scale purification of plasmid DNA

Extraction of plasmid DNA using reactor scale alkaline lysis and selective precipitation for scalable transient transfection

DNA extracted and purified for vaccination, gene therapy or transfection of cultured cells has to meet different criteria. We describe herein, a scalable process for the primary extraction of plasmid DNA suitable for transient expression of recombinant protein. We focus on the scale up of alkaline lysis for the extraction of plasmid DNA from Escherichia coli, and use a simple stirred tank reactor system to achieve this. By adding a series of three precipitations (including a selective precipitation step with ammonium acetate) we enrich very quickly the plasmid DNA content in the extract. The process has been thus far used to extract up to 100 mg of plasmid from 1.5 l of clarified lysate, corresponding to an E.coli bioreactor fermentation of 3 l.

Construction of a Co1E1 plasmid bearing inducible high-copy-number phenotype

In order to construct plasmids bearing inducible high-copy-number phenotype, the cloning plasmid pBR322 was modified as follows: a DNA fragment containing a strong synthetic promoter (P1), synthetic lac operator (O1), DNA sequence corresponding to the RNAI/RNAII region of the Co1E1 replicon and the CAT gene transcription terminator was substituted for the 29 bp EcoRI/HindIII DNA fragment. Two types of plasmids were constructed in this way, differing in the orientation of the RNAI/RNAII fragment. Depending on the orientation these plasmids coded for RNA molecules representing either RNAI or RNAII domains. It was found that when RNAII molecules were overproduced the plasmid copy number was about 4 times higher than that of pBR322 and only negligible change in the plasmid copy-number value was observed upon overproduction of RNAI molecules.

Expression of synthetic calcitonin genes in plasmid vectors containing tandemly repeated non-overlapping ribosome binding sites

1. Expression plasmids containing non-overlapping tandemly repeated ribosome binding sites (RBS) were constructed in order to stabilize mRNA and enhance translation. 2. Two synthetic genes (human calcitonin tetramer gene and a fusion gene human gamma-interferon-human calcitonin) were cloned in these vectors and the effect of multiplicity of Shine-Dalgarno (S/D) sequence on heterologous gene expression was studied. 3. It was found that duplication and triplication of RBS had no effect on the stability of mRNA but led to a strong decrease in the level of recombinant protein and mRNA in the cell. 4. Plasmids bearing four times repeated S/D sequences gave longer-lived mRNAs and maintained a level of protein and mRNA very close to the values obtained with a single S/D containing plasmids.

Constitutive expression of a native human interferon-alpha 1 gene in Escherichia coli

1. A plasmid for constitutive expression of the human interferon-alpha 1 (hIFN-alpha 1) gene in Escherichia coli is constructed on the basis of the cloning plasmid pBR322 using a strong synthetic promoter, synthetic ribosome binding site and a native hIFN-alpha 1 gene excised from a chromosomal clone. 2. The yield of recombinant hIFN-alpha 1 from E. coli LE392 cells transformed with the expression plasmid pJP1R9-hIFN-alpha 1 is evaluated to be 2-6 x 10(7) U/l bacterial culture for metabolic shaker and 6-8 x 10(7) U/l for fermentor.

Sequence heterogeneity of the human alphoid satellite DNA and thermal stability of mismatched alphoid DNA duplexes

1. 340 bp (dimer) and 680 bp (tetramer) fractions of the human alphoid satellite DNA (h alpha RI DNA) were isolated after complete cleavage of total human DNA with EcoR I and cloned in pBR 32.5. 2. Ten clones containing 340 bp inserts and one clone containing 680 bp insert were sequenced in order to investigate the sequence heterogeneity of this satellite DNA and the sequence data were compared with the consensus h alpha RI DNA sequence of Wu and Manuelidis (1980). 3. It was shown that in all clones studied the mutations are nonrandomly distributed along the human alphoid monomers forming distinct conservative and variable regions. 4. This mutation distribution pattern was compared with the nucleotide variations between the consensus sequences of different primate alphoid DNAs and it was found that the interspecies nucleotide divergency of this satellite DNA is quite similar to the intragenomic one. 5. The sequenced h alpha RI DNA clones were used for preparation of DNA-DNA hybrids with a known percentage of base pair mismatching. 6. These hybrids were melted on hydroxyapatite (HAP) and the results obtained were used to determine the relationship between the thermal stability (Tm) and the extent of base pair mismatching for naturally diverged DNA sequences. 7. A value of 0.7 degrees C decrease in Tm per 1% base pair mismatching was found.