Fig. 8.

The molecular-structures of B–A and B–B premeltons. To simulate these structures, base-paired dinucleotide-elements obtained from the modeling-studies described in Fig. 7a, b, were pieced-together using a least-squares procedure. It is seen that, whereas B-A premeltons are (globally) topological, B–B premeltons are (globally) nontopological—this reflects the presence of a bifurcation—which gives rise to these two different-types of structural-solitons in DNA. See text for further discussion