title: Unique structures formed by pyrimidine-purine DNAs which may be four-stranded.
abstract: Pyrimidine-purine DNAs with repeating sequences can be made to undergo a reversible transition to possibly a tetra-stranded complex. Physicochemical characterization of the new structures and model building are consistent with, in the case of d(TC)n-d(GA)n, a tetra-stranded complex forming by the addition of d(GA)n to the remaining space in the major groove of the triple-stranded complex d(TC)n-d(GA)n-d(CT)n. A possible role for tetra-stranded complexes in chromosome condensation is suggested by the natural occurrence of repeating sequence pyrimidine-purine DNAs and the properties of condensed chromosomes.
mesh_terms: D001483:Base Sequence; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002875:Chromosomes / Q000648:ultrastructure; D004247:DNA; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D011687:Purines; D011743:Pyrimidines
chemical_list: D011687:Purines; D011743:Pyrimidines; D004247:DNA
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