title: Extension of the four-stranded intercalated cytosine motif by adenine.adenine base pairing in the crystal structure of d(CCCAAT).
abstract: The crystal structure of d(CCCAAT), refined at 2.0 A resolution, shows a four stranded molecule in which two parallel duplexes intercalate with opposite polarity, using cytosine.protonated cytosine base pairs. The intercalation motif in this structure is extended by adenine.adenine base pairs. Two topologically distinct broad grooves are found in the lath-like central part of the molecule with the phosphate groups on one side bent over towards each other, stabilized by bridging water molecules. At the 3' ends, two arrangements of intermolecular A.A.T base triplets are found, involving both asymmetric and symmetric A.A base pairs joined to thymine residues by Watson-Crick and reverse Hoogsteen base pairing, respectively.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA.
authors.forename: I
authors.initials: I
authors.lastname: Berger
authors.forename: C
authors.initials: C
authors.lastname: Kang
authors.forename: A
authors.initials: A
authors.lastname: Fredian
authors.forename: R
authors.initials: R
authors.lastname: Ratliff
authors.forename: R
authors.initials: R
authors.lastname: Moyzis
authors.forename: A
authors.initials: A
authors.lastname: Rich
mesh_terms: D000225:Adenine / Q000737:chemistry; D001482:Base Composition; D001483:Base Sequence; D018360:Crystallography, X-Ray; D003596:Cytosine / Q000737:chemistry*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009711:Nucleotides / Q000737:chemistry*
chemical_list: D009711:Nucleotides; D003596:Cytosine; D000225:Adenine