EFFECT OF SELECTIVE SUBSTITUTION OF 5-BROMOCYTOSINE ON CONFORMATION OF DNA TRIPLE HELICES

Three tripler DNAs containing 5-bromocytosine[C-Br] were studied by vi brational spectroscopy and molecular modelling. Firstly, three oligode oxypyrimidines of 5'-(TC)3-T4-((CT)-C-Br)3 [(CC)-C-Br], 5'-((TC)-C-Br) 3-T4-(CT)3 [(CC)-C-Br] and 5'-((TC)-C-Br)3-T4-((CT)-C-Br)3 [(CC)-C-Br- C-Br] were synthesized and then reacted with an oligodeoxypurine of 5' -(AG)(3) at pH=4.5 in phosphate buffer respectively to form three comp arative hairpin tripler named CY,YC and YY. The results of FT-Raman an d IR revealed that YY is almost in A-like form, CY and YC are combinat ions of A-like form and B-like form, but A-form dominates in CY while B-form is equivalent as A-form in YC. The result is consistent with th e theoretical analysis.