title: Flexibility of A.T pairs in left-handed DNA helices.
abstract: We have analysed by various approaches the structure of cloned synthetic sequences in supercoiled plasmids. Individual inserts were formed by d(C-G)n blocks interrupted by the presence of A.T pairs positioned either in phase or out of phase of pur-pyr alternation. Based on the thermodynamic analysis we obtained results confirming that A.T pairs are easily incorporated into left-handed helices without significant energetic penalty. Sequences GTAC which are known to form cruciform structures in multiple repetition underwent a B-Z transition. In the case of plasmids containing AA/TT code words and substantial discontinuities in purine-pyrimidine alternation our analysis indicates that Z-Z junctions formed by A.T pairs contributed little to the overall energetic demands of the B-Z transition probably thanks to their high conformational flexibility.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, Prague.
authors.forename: J
authors.initials: J
authors.lastname: Vlach
authors.forename: J
authors.initials: J
authors.lastname: Sponar
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D004247:DNA / Q000648:ultrastructure*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D013816:Thermodynamics
chemical_list: D004247:DNA