Aptamer is presented as a composite BB of two half-schemes, which is representative for the organization of aptamers. The inset shows the internal structure of each half-scheme of the Sassanfar–Szostak motif [ 85 , 86 ]. See text for details. All the domains are assumed to be identic. (B-C) Structural details of conservative functional regions of an aptamer using Sassanfar–Szostak motif as an example: (B) 2D structure and (C) nucleotide sequence. Positions in the recognition bulge are colored according to whether they are invariant (red), two-base varying (green), or non-conserved (black). Here …xxxxx corresponds to the halves of the insulating spacer sequences, NNNNN & nnnnn are the complementary halves of the sequences of the first and second stem, ** …** is arbitrary and corresponds to the closing loop sequence. (D) 26 nucleotide core part of the Sassanfar-Szostak motif implemented in our BioRS as a consensus. Four G-nucleotides of this consensus are single-valued (red), 10 loci are defined up to nucleotide pairs (blue), while the rest are assumed arbitrary (N or n, in black).