The 31P-NMR spectrum of the dodecamer d(GACGATATCGTC).

The resonances in the 31P-NMR spectrum of the dodecamer d(GACGATATCGTC) have been assigned by regiospecific labelling with oxygen-17. All 11 resonances are clearly resolved at 26 degrees C. Most noticeably, individual resonances of the dinucleoside phosphates d(CpG), d(TpC), d(GpA) and d(ApT) which occur more than once can clearly be distinguished. This indicates that the position of the phosphate group in the oligomer influences its 31P-NMR shift. This observation is in agreement with what has been found for the 31P-NMR spectra of d(CGCGAATTCGCG) [Ott, J. and Eckstein, F. (1985) Biochemistry 24] and d(GGAATTCC) [Connolly, B.A. and Eckstein, F. (1984) Biochemistry 23, 5523-5527]. In general, the chemical shift appears the more at higher field the more central the dinucleoside phosphate is located in the oligomer. Exceptions are the resonances of dinucleoside phosphates of the type 5'-PyPu-3' which appear at lower field than expected from this rule. A reasonable correlation between 31P-NMR chemical shifts and the sum function of the base plane roll angles derived from Calladine's rule [Calladine, C.R. (1982) J. Mol. Biol. 161, 343-352] exists.