An analysis of the stability of a duplex containing G x A mispairs or G x A/A x G tandem during the DNA melting has shown that the duplex stability depends on both DNA sequences and the conformations of the G x A mispairs. The thermodynamics of single pair opening for the G(anti) x A(syn) and G(anti) x A(anti) conformations adopted by a G x A mispair is found to strongly correlate with that of the canonical base pairs, while for the sheared conformation a significant difference is observed.