Purification of mycobacterial deoxyribonucleic acid.

Impurities believed to be polysaccharides have been found in mycobacterial deoxyribonucleic acid (DNA) preparations. Agar-gel diffusion of the DNA preparations against concanavalin A indicated the presence of three polysaccharides and was used to follow the purification procedures. The polysaccharides appeared to be the same for all strains studied. Precipitation of DNA with cetyltrimethylammonium bromide was used to separate impurities from some DNA preparations. The presence of the contaminants was found to affect markedly the determination of the guanine plus cytosine content according to a method dependent on the ratio of absorbancies at 260 and 280 nm; the impurities did not affect the determination by the method of thermal denaturation. The presence of a DNA-polysaccharide complex is suggested.