Strategy for DNA synthesis by ligation of octamers. (a) Experimental design a DNA adaptor containing a BbsI restriction site at the ligation end. An immobilized product can be purified through washing and released through BbsI digestion while maintaining a 4-nt overhang allowing it to be used in further ligation reactions. (b) Mapping of target construct into four 32-bp fragments. Each fragment is made of eight octamers and has ends complementary to the next fragment in the series. (c) Schematic overview of the pair-wise construction process. Four groups of octamers are ligated in pooled reactions to produce 32-bp intermediates as outlined in (b). Selected intermediates are then mobilized and ligated to neighboring fragments. A second round repeats the process to produce one fragment containing all four intermediates.