Case (iv): E AA =E BB =0, and E AB =-2. This represents the inverse of case (iii). In case (iv) the two building blocks have a strong affinity for each other, while self-interactions are weak. The optimal organization of building blocks along the axis of the replicator fiber would be in alternating manner (ABAB…). Nucleobases interacting through Watson-Crick base pairing resemble such interaction motif.