Flanking AT-rich tracts cause a structural distortion in Z-DNA in plasmids.
The effect of neighboring AT-rich sequences on the right-handed B to left-handed Z transition was investigated in plasmids. The supercoil stabilized Z-DNA structure in (CG) tracts 36 and 40 base pairs (bp) in length revealed an unexpected conformational aberration at defined C residues proximal to one end (colL) when the inserts were bilaterally flanked by an 80% AT-rich segment (90 bp on one side and 331 bp on the other). The presence of the perturbed Z-conformation required (CG) stretches longer than 32 bp and bilateral flanking by the AT-rich tracts, since plasmids with the (CG) tracts unilaterally flanked had an orthodox Z-structure. The thermodynamics of the negative super-coil-induced transitions were influenced only slightly by the neighboring AT-rich regions. Hence, the nature of Z-conformations in plasmids is markedly influenced by intrinsic structural features of the (Pur-Pyr) tract and by seemingly modest changes in the properties of neighboring sequences over a distance of several helical turns.
University of Alabama, Department of Biochemistry, School of Medicine, Birmingham 35294.
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Rajagopalan
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Rahmouni
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Wells
D000225:Adenine; D001482:Base Composition; D001483:Base Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000737:chemistry*; D005822:Genetic Vectors; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010957:Plasmids; D015183:Restriction Mapping; D013941:Thymine
D004247:DNA; D000225:Adenine; D013941:Thymine