On the metastability of left-handed DNA motifs.
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.
Reich
Z
Z
Department of Organic Chemistry, Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel.
Friedman
P
P
Scolnik
Y
Y
Sussman
J L
JL
Minsky
A
A
D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D007700:Kinetics; D015636:Magnesium Chloride; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000138:chemical synthesis / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
D009838:Oligodeoxyribonucleotides; D015636:Magnesium Chloride; D004247:DNA