a1 CRC Nucleic Acid Structure Group, Department of Biochemistry, The University, Dundee DD1 4HN, U.K.
a2 Abteilung Molekulare Biologie, Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg, D-3400 Göttingen, Federal Republic of Germany
Branched DNA molecules provide a challenging set of structural problems. Operationally we define branched DNA species as molecules in which double helical segments are interrupted by abrupt discontinuities, and we draw together a number of different kinds of structure in the class, including helical junctions of different orders, and base bulges (Fig. 1).