There are a couple of things that our lab looks for when we buy plasmid purification kits. They should be fast, simple and reliable and should be able to purify relatively large amounts of plasmid DNA from a bacterial culture. Several major brands, including Clontech, a Takara Bio Company, offers kits that fit these requirements. They are all based on the same principle and follow the same general scheme: bacteria lysis, plasmid purification by chromatography on anion exchanger, elution of the plasmid. There are, however, subtle differences among brands (e.g. the chemical composition of the resin) that are critical in terms of both quantity and quality of the DNA preparations.
I routinely do maxi preps and several months ago I began using the Nucleobond Plasmid Maxi Kit. One of the main reasons that I started using these kits is the very competitive price (I suggest contacting Clontech and asking for a quote, especially if you are going to be performing lots of plasmid preps). Before I began exclusively using the Nucleobond kits, I did some comparisons with other kits, splitting bacteria cultures in two and doing side-by-side preparations. The results for both low and high molecular weight plasmids were similar in terms of both yield and purity of DNA. In the end, I preferred the Nucleobond Plasmid Maxi Kit because (in addition to the price): 1) the preparation was quick - about 20 min faster than other kits; 2) the columns did not release any material during the DNA elution. The latter issue is an annoying, still common problem when dealing with some maxi kits and it must affect the quality of DNA.
Some of the other features that I liked about the Nucleobond kits are the reliably high yield (truly 500 micrograms for high copy plasmids, as advertised by the manufacturer) and a very high transfection efficiency. I am not sure why the transfection efficiency for DNA prepped with this kit is so high, but other colleagues on my floor have noticed the same thing. One of the features that I dislike about the Nucelobond kit is a detail in the column design: the column holders do not hold and I need to tape the columsn to it. Some of the competing columns have a more practical shape.
In summary, I would say the Clontech Nucleobond Plasmid Maxi Kit is one of the best kit for "maxi" preparations of plasmid DNA I have ever used. It is cheaper (at least for our institution – pricing can vary), faster and more efficient than other systems: everything our lab was looking for in a plasmid prep kit.
Dario Coletti, PhD
Post-Doctoral Fellow
Mount Sinai School of Medicine
New York, NY