Using dot-parens-plus notation, each unpaired base is represented by a dot, each base pair by matching parentheses, and each nick between strands by a plus (Zadeh et al., J Comput Chem , 2011).
Using DU+ notation, a duplex of length x base pairs is represented by Dx and an unpaired region of length x nucleotides is represented by Ux (Zadeh, PhD Thesis, California Institute of Technology, 2011). Each duplex is followed immediately by the substructure (specified in DU+ notation) that is 'enclosed' by the duplex. If this substructure includes more than one element, parentheses are used to denote scope. A nick between strands is specified by a '+'. For example:
x
is denoted ..(((...((((((..+.)))))).((((....))))))) in dot-parens-plus notation and U2 D3 (U3 D6 (U2 + U1) U1 D4 (U4)) in DU+ notation.
..(((...((((((..+.)))))).((((....)))))))
U2 D3 (U3 D6 (U2 + U1) U1 D4 (U4))