The B-A transition in superhelical DNA.
Relaxation of a DNA superhelical stress due to the B to A transition induced by trifluoroethanol has been studied by assessing the change of DNA orientation in a flow gradient. Using DNAs of different superhelical densities, a decrease in the winding angle during the B----A shift of DNA was found to be 1.5 degrees per base pair in solution. Accepting the winding angle for B-DNA in solution to be 34.1 degrees, that for A-DNA must have a value of 32.6 degrees which agrees with the X-ray data for A-DNA in the condensed state. The date obtained within the B-A transition interval make it possible to conclude that there is an increase in winding at each B/A junction, which is about 5 degrees per one junction.
Krylov DYu
Engelhardt Institute of Molecular Biology, USSR Academy of Sciences, Moscow.
Makarov
V L
VL
Ivanov
V I
VI
D004264:DNA Topoisomerases, Type I; D004270:DNA, Circular; D004996:Ethidium; D007700:Kinetics; D009690:Nucleic Acid Conformation; D010957:Plasmids
D004270:DNA, Circular; D004264:DNA Topoisomerases, Type I; D004996:Ethidium