Lane A N, Bauer C J, Frenkiel T A
Laboratory of Molecular Structure, National Institute for Medical Research, The Ridgeway, Mill Hill, London.
Eur Biophys J. 1993;21(6):425-31. doi: 10.1007/BF00185870.
Rotating-frame relaxation measurements have been used in conjunction with spin-spin relaxation rate constants to investigate a conformational transition previously observed in the -10 region of the trp promoter d(CGTACTAGTTAACTAGTACG)2 (Lefèvre, Lane, Jardetzky 1987). The transition is localised to the sub-sequence TAAC, and is in fast exchange on the chemical shift time-scale. The rate constant for the exchange process has been determined from measurements of the rotating-frame relaxation rate constant as a function of the spin-lock field strength, and is approximately 5000 s-1 at 30 degrees C. Measurements have also been made as a function of temperature and in two different magnetic fields: the results are fully consistent with those expected for the exchange contribution in a two-site system. A similar transition has been observed in d(GTGATTGACAATTA).d(CACTAACTGTTAAT), which contains the -35 region of the trp promoter. This has been investigated in the same way, and has been found to undergo exchange at a faster rate under comparable conditions. In addition, the cross-relaxation rate constants for Ade C2H-Ade C2H pairs have been measured as a function of temperature, and these indicate that certain internuclear distances in YAAY subsequences increase with increasing temperature. These changes in distance are consistent with a flattening of propellor twist of the AT base-pairs. The occurrence of conformational transitions in YAAY subsequences depends on the flanking sequence.
旋转框架弛豫测量已与自旋-自旋弛豫速率常数结合使用，以研究先前在色氨酸启动子d（CGTACTAGTTAACTAGTACG）2的-10区域观察到的构象转变（勒费弗尔、莱恩、雅德茨基，1987年）。该转变局限于子序列TAAC，并且在化学位移时间尺度上处于快速交换状态。交换过程的速率常数已通过测量旋转框架弛豫速率常数作为自旋锁定场强的函数来确定，在30℃时约为5000 s-1。还进行了作为温度函数以及在两个不同磁场中的测量：结果与两点系统中交换贡献预期的结果完全一致。在包含色氨酸启动子-35区域的d（GTGATTGACAATTA）.d（CACTAACTGTTAAT）中观察到了类似的转变。已以相同方式对其进行了研究，发现在可比条件下其交换速率更快。此外，已测量了腺嘌呤C2H-腺嘌呤C2H对的交叉弛豫速率常数作为温度的函数，这些结果表明YAAY子序列中的某些核间距离随温度升高而增加。这些距离变化与AT碱基对的螺旋桨扭转变平一致。YAAY子序列中构象转变的发生取决于侧翼序列。
