Effect of Hg(II) on the spectroscopic properties of poly[d(A-T).d(A-T] and poly[d(A).d(T)] and their constituent subunits (deoxyadenosine and thymidine monomers and dimers).

Adding, respectively, increasing amounts of Hg(ClO4)2 (identical to Hg(II)) to poly[d(A-T).d(A-T)] (I), poly[d(A).d(T)] (II) as well as to their constituent subunits 2'-deoxyadenosine (identical to dA), thymidine (identical to dT), 2'-deoxyadenosine-5'- monophosphate (identical to dAp), thymidine-5'-monophosphate (identical to dTp), 2'-deoxyadenylyl-(3'-->5')-2'-deoxyadenosine (identical to d(ApA)), 2'-deoxyadenylyl-(3'-->5')-thymidine (identical to d(ApT)), thymidylyl- (3'-->5')-2'-deoxyadenosine (identical to d(TpA)), and thymidylyl- (3'-->5')-thymidine (identical to dTpT))--all dissolved in 0.1 M NaClO4, 5 mM cacodylic acid, pH 7--generates changes in their UV spectra that (a) progress in (I) in a pattern that is distinctly different from the one occurring in (II) and that (b) reveal a strong sequence dependence in the case of the dinucleoside phosphates. The spectroscopic parameters D (dipole strength), f (oscillator strength), and h (hypochromicity) were determined as a function of Hg(II) concentration for both polymers as well as for all dimers. Also determined were D and f of the monomers. D and f of dA, dAp, and d(ApA) display a different dependence on Hg(II) concentration than do D and f of dT, dTp, and d(TpT). The corresponding parameters of the mixed-sequence dimers d(ApT) and d(TpA) vary with Hg(II) in a 'mirror'-like fashion. Increase in base stacking subsequent to mercury binding is noted with d(TpT) and d(TpA). The opposite occurs in d(ApT). Hg(II) exerts only marginal effects on the base stacking in d(ApA). Both D and f of polymers (I) and (II) increase with increasing levels of Hg(II), i.e. Hg(II) binding decreases base stacking (loss of hypochromicity).(ABSTRACT TRUNCATED AT 250 WORDS)