The purine 2-amino group as a critical recognition element for binding of small molecules to DNA

The expedient of preparing homologous DNA samples substituted with I for G, DAP for A, or both, has been used to investigate the role of the purine 2-amino group in determining the preferred binding sites for antibiotics on DNA. The selectivity of echinomycin for CpG steps, of actinomycin for GpC steps, and of netropsin for A + T-rich tracts, is seen to be radically altered in the substituted DNA molecules.