Synthesis and physical characterization of the self-complementary, alternating pyrimidine/purine hexanucleotide d[CGTACG].

The hexanucleotide d(CGTACG) has been synthesized by a phosphotriester method in which, for the first time, an O-6 protected deoxyguanosine derivative has been used to avoid side reactions of the guanine residues. Conformational analysis by circular dichroism shows that d(CGTACG) maintains a B form under conditions (5 M NaCl) where the all C/G hexanucleotide d(CG)3 adopts a Z form, even though d(CGTACG) is a fully alternating pyrimidine/purine molecular. The delta H for the helix-to-coil transition has been measured.