Flipping of cloned d(pCpG)n.d(pCpG)n DNA sequences from right- to left-handed helical structure by salt, Co(III), or negative supercoiling.
Negative supercoiling of plasmid DNAs containing 24--42 base pairs of alternating d(pCpG) inserts is shown to cause the flipping of the helical hand of the inserts from right to left under physiological conditions. For a negatively supercoiled DNA with a fixed linking number, this flipping reduces its superhelicity and, therefore, is accompanied by a shift of its electrophoretic mobility in agarose gel. Quantitation of the mobility shifts indicates that essentially the whole stretch of contiguous alternating d(pCpG) flips to the left-handed helical form when the negative superhelical density (specific linking difference) is greatest than or equal to 0.03.
D001483:Base Sequence; D003001:Cloning, Molecular; D003035:Cobalt / Q000494:pharmacology; D004278:DNA, Superhelical; D008970:Molecular Weight; D009690:Nucleic Acid Conformation / Q000187:drug effects; D009994:Osmolar Concentration; D010957:Plasmids; D013329:Structure-Activity Relationship
D004278:DNA, Superhelical; D003035:Cobalt