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DNA purification - long fragments wanted - (Mar/13/2009 )

I am purifying bacterial genomic DNA using kits from both Invitrogen and Qiagen. However these kits have a tendency to produce fragments in the length of 20-30 kb in length and in a particular project I am looking for longer product in lengths of preferebly 50-60 kb.
So far I have identified a possible product from Macherey-Nagel, NucleoBond AXG. Does anyone have experience with this kit or other protocols that allow a more gentle genomic DNA purification method?



A phenol/chloroform extraction and ethanol precipitation will produce long fragments, if you are careful not to vortex the sample. Embedding the sample in agarose and treating with lysozyme/proteinase-k/SDS will lyse the cells and leave intact long molecules. See the preparation techniques for pulse field gel electrophoresis.