Fragmented denatured total DNA of Salmonella typhimurium can be separated on methylated albumin kieselguhr columns into two fractions by the intermittent gradient elution technique, or into several fractions by increasing the salt concentration of the eluting buffer stepwise. The fractionation is based mainly on differences of nucleotide composition, fragments with high Pu/Py ratio are eluted at lower salt concentrations. In contrast to the similar fractionation of Bacillus subtilis DNA, this procedure does not lead to the separation of all the complementary DNA strands. Only those fragments, which exhibit higher than average asymmetry in the Pu/Py ratio, such as the DNA sequences coding for ribosomal RNA, can be separated into complementary strands by either of the two procedures.
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