ON THE PAIRING RULES FOR RECOGNITION IN THE MINOR-GROOVE OF DNA BY PYRROLE-IMIDAZOLE POLYAMIDES

Background: Cell-permeable small molecules that target predetermined D NA sequences with high affinity and specificity have the potential to control gene expression, A binary code has been developed to correlate DNA sequence with side-by-side pairings between N-methylpyrrole (Py) and N-methylimidazole (Im) carboxamides in the DNA minor groove, We se t out to determine the relative energetics of pairings of Im/Py, Py/Im , Im/Im, and Py/Py for targeting G.C and A.T base pairs. A key specifi city issue, which has not been previously addressed, is whether an Im/ Im pair is energetically equivalent to an Im/Py pair for targeting G.C base pairs. Results: Equilibrium association constants were determine d at two five-basepair sites for a series of four six-ring hairpin pol yamides, in order to test the relative energetics of the four aromatic amino-acid pairings opposite G.C and A.T base pairs in the central po sition, We observed that a G.C base pair was effectively targeted with Im/Py but not Py/Im, Py/Py, or Im/Im. The A.T base pair was effective ly targeted with Py/Py but not Im/Py, Py/Im, or Im/Im. Conclusions: An Im/Im pairing is energetically disfavored for the recognition of both A.T and G.C. This specificity will create important limitations on un desirable slipped motifs that are available for unlinked dimers in the minor groove. Baseline energetic parameters will thus be created whic h, using the predictability of the current pairing rules for specific molecular recognition of double-helical DNA, will guide further second -generation polyamide design for DNA recognition.