It has previously been demonstrated by other workers that the duplex of a synthetic DNA poly(amino2dA-dT) undergoes a salt-induced conformational isomerization. We show in the present work using circular dichroism that the same isomerization is induced in poly(amino2dA-dT) by various alcohols. The isomerization was originally identified as the B-to-Z and then B-to-A conformational transition of DNA but we demonstrate that the high-salt or alcohol conformation of poly (amino2dA-dT) is the non Z-DNA zig-zag double helix we have previously observed with poly(dA-dT) and called X-DNA. X-DNA is a cesium cation specific conformation of poly(dA-dT) while no similar cation specificity is observed with poly(amino2dA-dT). Thus it appears that the extra amino group attached to A and cesium cations make the same thing; they probably dehydrate the double helix minor groove and relieve its conformational variability. Poly(amino2dA-dT) is exceptionally stable in X-DNA and conditions inducing it are mild, which opens the door to assess its molecular structure.

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The chemical synthesis of 5-alkyl-dUTP-s and their participation as substrates in poly[d(A-6)] primed polymerization reactions with dATP by E. coli DNA polymerase I enzyme has been described. In comparison with dTTP, at saturating substrate concentrations, the rate of hypochromic effect was found to be 17.3% higher for dUTP and was lower by 27.4% for 5-ethyl-dUTP, 29.5% for 5-n-propyl-dUTP, 31.4% for 5-n-butyl-dUTP and by 85.0% for 5-n-pentyl-dUTP. No hypochromic effect could be observed, however, with 5-iso-propyl-, 5-tert.butyl- and 5-n-hexyl-dUTP-s. Polydeoxynucleotides have also been isolated from the reaction mixture and some of their structural properties determined.