Reich Z, Friedman P, Scolnik Y, Sussman J L, Minsky A
Department of Organic Chemistry, Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel.
Biochemistry. 1993 Mar 2;32(8):2116-9. doi: 10.1021/bi00059a033.
Alternating purine-pyrimidine DNA sequences such as poly [d(C-G)] or poly[d(m5C-G)] undergo a cooperative, salt-induced structural transition from a right-handed B conformation, which prevails at relatively low ionic strength, into a left-handed Z form, generally believed to be stabilized by high salt concentrations. We report here that upon a monotonous increase of the ionic strength, the well-established B to Z transition is followed by a second, hitherto unobserved conformational change leading from Z-DNA back into a right-handed B-like form. This observation indicates that, in contrast with the current convention, the Z motif represents an unstable configuration relative to the B form at both low and high salt concentrations and that the occurrence of a left-handed DNA structure, presently depicted as a step function of the ionic strength, should rather be treated in terms of a pulse. The reported transition underscores the inherent metastability of the Z configuration, and indicates, consequently, that this motif is ideally suited to act as a structural regulatory element, as such an element should be endowed with a large susceptibility to cellular parameters.
交替的嘌呤 - 嘧啶DNA序列，如聚[d（C - G）]或聚[d（m5C - G）]，会经历一种协同的、盐诱导的结构转变，从在相对低离子强度下占主导的右手B构象转变为左手Z构象，一般认为高盐浓度会使其稳定。我们在此报告，随着离子强度单调增加，已确立的B到Z转变之后会发生第二种迄今未观察到的构象变化，导致从Z - DNA变回右手类似B的形式。这一观察结果表明，与当前的传统观点相反，在低盐和高盐浓度下，Z基序相对于B形式代表一种不稳定的构型，并且目前被描绘为离子强度阶跃函数的左手DNA结构的出现，更应该被视为一种脉冲。所报道的转变强调了Z构型固有的亚稳定性，因此表明该基序非常适合作为一种结构调节元件，因为这样的元件应该对细胞参数具有很大的敏感性。
