The specific-sequence domains of T x y can trigger the dimerization of a specific M x L , N y pair from pools of monomers in solution. The result is a product distribution enriched in M x N y dimers with t and h domains (red boxes) complementary to T x y , propagating the sequence information in the template. Any x , y combination is possible, with the dimerization domain a initially hidden by L , inhibiting any direct reaction in the absence of T x y . The edges of the M x L duplex have additional bases—‘clamps’—suppressing any leak reactions. The two mismatched base pairs in the a domain of M x L ensure that dimerization is thermodynamically favoured. The DNA strands are represented by domains (contiguous sequences of nucleotides considered to hybridize as a unit). The domains are labelled with a lowercase letter; a prime symbol indicates complementarity; for example, a′ binds to a.
