Patel D J, Kozlowski S A, Ikuta S, Itakura K
Biochemistry. 1984 Jul 3;23(14):3207-17. doi: 10.1021/bi00309a015.
Nuclear magnetic resonance (NMR) has been used to monitor the conformation and dynamics of the d-(C1-G2-A3-G4-A5-A6-T6-T5-C4-G3-C2-G1) self-complementary dodecanucleotide (henceforth called 12-mer GA) that contains a dG X dA purine-purine mismatch at position 3 in the sequence. These results are compared with the corresponding d(C-G-C-G-A-A-T-T-C-G-C-G) dodecamer duplex (henceforth called 12-mer) containing standard Watson-Crick base pairs at position 3 [Patel, D.J., Kozlowski, S.A., Marky, L.A., Broka, C., Rice, J.A., Itakura, K., & Breslauer, K.J. (1982) Biochemistry 21, 428-436]. The dG X dA interaction at position 3 was monitored at the guanosine exchangeable H-1 and nonexchangeable H-8 protons and the nonexchangeable adenosine H-2 proton. We demonstrate base-pair formation between anti orientations of the guanosine and adenosine rings on the basis of nuclear Overhauser effects (NOE) observed between the H-2 proton of adenosine 3 and the imino protons of guanosine 3 (intra base pair) and guanosines 2 and 4 (inter base pair). The dG(anti) X dA(anti) pairing should result in hydrogen-bond formation between the guanosine imino H-1 and carbonyl O-6 groups and the adenosine N-1 and NH2-6 groups, respectively. The base pairing on either side of the dG X dA pair remains intact at low temperature, but these dG X dC pairs at positions 2 and 4 are kinetically destabilized in the 12-mer GA compared to the 12-mer duplex. We have estimated the hydrogen exchange kinetics at positions 4-6 from saturation-recovery measurements on the imino protons of the 12-mer GA duplex between 5 and 40 degrees C. The measured activation energies for imino proton exchange in the 12-mer GA are larger by a factor of approximately 2 compared to the corresponding values in the 12-mer duplex. This implies that hydrogen exchange in the 12-mer GA duplex results from a cooperative transition involving exchange of several base pairs as was previously reported for the 12-mer containing a G X T wobble pair at position 3 [Pardi, A., Morden, K.M., Patel, D.J., & Tinoco, I., Jr. (1982) Biochemistry 21, 6567-6574]. We have assigned the nonexchangeable base protons by intra and inter base pair NOE experiments and monitored these assigned markers through the 12-mer GA duplex to strand transition.(ABSTRACT TRUNCATED AT 400 WORDS)
核磁共振（NMR）已被用于监测d-（C1-G2-A3-G4-A5-A6-T6-T5-C4-G3-C2-G1）自互补十二聚体核苷酸（以下简称12聚体GA）的构象和动力学，该序列在第3位含有一个dG×dA嘌呤-嘌呤错配。将这些结果与相应的在第3位含有标准沃森-克里克碱基对的d（C-G-C-G-A-A-T-T-C-G-C-G）十二聚体双链体（以下简称12聚体）进行比较[帕特尔，D.J.，科兹洛夫斯基，S.A.，马尔基，L.A.，布罗卡，C.，赖斯，J.A.，伊塔库拉，K.，&布雷斯劳尔，K.J.（1982年）《生物化学》21，428 - 436]。在鸟苷可交换的H-1和不可交换的H-8质子以及不可交换的腺苷H-2质子处监测第3位的dG×dA相互作用。基于腺苷3的H-2质子与鸟苷3（碱基对内）和鸟苷2及4（碱基对间）的亚氨基质子之间观察到的核Overhauser效应（NOE），我们证明了鸟苷和腺苷环反式构象之间的碱基对形成。dG（反式）×dA（反式）配对应分别导致鸟苷亚氨基H-1与羰基O-6基团以及腺苷N-1与NH2-6基团之间形成氢键。dG×dA对两侧的碱基对在低温下保持完整，但与12聚体双链体相比，12聚体GA中第2和4位的这些dG×dC对在动力学上不稳定。我们通过在5至40摄氏度之间对12聚体GA双链体亚氨基质子的饱和恢复测量估算了第4至6位的氢交换动力学。12聚体GA中亚氨基质子交换的测量活化能比12聚体双链体中的相应值大约大2倍。这意味着12聚体GA双链体中的氢交换是由涉及几个碱基对交换的协同转变引起的，正如之前报道的在第3位含有G×T摆动对的12聚体[帕尔迪，A.，莫登，K.M.，帕特尔，D.J.，&蒂诺科，I.，Jr.（1982年）《生物化学》21，6567 - 6574]。我们通过碱基对内和碱基对间的NOE实验对不可交换的碱基质子进行了归属，并通过12聚体GA双链体监测这些归属标记直至链转变。（摘要截断于400字）
