Isolation of DNA from plant cells by gel filtration on agarose

A method is described which allows the obtention of total DNA from cells of Chlamydomonas reinhardi in 1 day. It is based on the gel filtration on agarose of crude lysates incubated for1 hr with pronase and subsequently brought to 2 m NaCl in order to dissociate nucleoprotein complexes. The DNA obtained in this way contains no detectable pigments nor RNA and is contaminated by less than 2% protein. The buoyant densities determined by CsCl density gradient centrifugation are 1.724 ± 0.002 and 1.695 ± 0.002 g/cm³ for nuclear and chloroplast DNA, respectively. A slight modification of the method makes it applicable to the extraction of DNA from Vigna mungo (Phaseolus aureus) whose buoyant density in a CsCl gradient is found to be 1.693 ± 0.002 g/cm³. The molecular weight of DNA extracted from both systems can be grossly estimated to be around 3-10 × 10⁶.