Effect of 5-alkyl substitution of uracil on the thermal stability of poly[d(A-r5U)] copolymers

Abstract

The thermal transition of poly[d(A-r⁵U)] polydeoxynucleotides (where r was a hydrogen atom, or a methyl, ethyl, n-propyl, n-butyl or n-pentyl group) was studied by measuring the derivative melting profiles of the polymers in the range of 0.01–0.36 M K⁺, at pH 6.8. According to the T_m values, polydeoxynucleotide analogues show lower thermal stability than poly[d(A-T)] at any counterion concentration applied. At a given salt concentration, T_m of the alkyl analogues decreased as the number of carbon atoms (n) in the r substituent of poly[d(A-r⁵U)] increased. 1/T_m plotted against 1/n yielded a linear relationship. Cooperativity of the melting of all poly[d(A-U)] analogues decreased with the increase of salt concentration in the solution. This change depended again on 5-substitution of the uracil moiety of poly[d(A-U)] Smallest decrease was observed in the case of poly[d(A-U)] whereas largest decrease was shown by poly [d(A-pe⁵U)] (pe=pentyl group)