Schiff base-mediated base pairing.

We here present a novel covalently linked base pair via Schiff base formation between 5-formyluracil (fU) and 5-aminocytosine (AmC). The formation of Schiff base remarkably increases thermal stability of the duplex DNA, whereas it completely dissociates upon heating at 90 degrees C. Neither AmC nor fU produces covalent linkage with other natural bases, and thus the pairing ability of AmC and fU is very specific.