title: The crystal structure of d(CCCCGGGG): a new A-form variant with an extended backbone conformation.
abstract: The crystal structure of d(CCCCGGGG) has been determined at a resolution of 2.25 A. The oligomers crystallize as A-DNA duplexes occupying crystallographic two-fold axes. The backbone conformation is, in general, similar to that observed in previously reported crystal structures of A-DNA fragments, except for the central linkage, where it adopts an extended structure resulting from all trans conformation at the P-O5'-C5'-C4' bonds. This type of conformation facilitates interstrand stacking between the guanines at the C-G site. The local helix twist at this step is very small (25 degrees) compared to an overall average of 33.5 degrees. The unique structure of the C-G base-pair step, namely the extended backbone and the distinct stacking geometry, may be an important feature in the recognition mechanism between double-stranded DNA molecules and restriction endonucleases such as Msp I, which cuts the sequence CCGG very specifically with a rate unaffected by neighboring base pairs.
authors.affiliation: Dept. of Structural Chemistry, Weizmann Institute of Science, Rehovot,Israel.
authors.forename: T E
authors.initials: TE
authors.lastname: Haran
authors.forename: Z
authors.initials: Z
authors.lastname: Shakked
authors.forename: A H
authors.initials: AH
authors.lastname: Wang
authors.forename: A
authors.initials: A
authors.lastname: Rich
mesh_terms: D004247:DNA / Q000648:ultrastructure*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000138:chemical synthesis; D014961:X-Ray Diffraction
chemical_list: D009838:Oligodeoxyribonucleotides; D004247:DNA