Crystal structure of a four-stranded intercalated DNA: d(C4)
THIS IS THE FIRST X-RAY STRUCTURE OF THE INTERCALATED CYTOSINE QUADRUPLEX. THE PAPER CITED IN JRNL DESCRIBED THE D(C4) STRUCTURE REFINED AT 2.3 ANGSTROMS RESOLUTION. THE AUTHORS HAVE EXTENDED THE STRUCTURE DETERMINATION TO 1.8 ANGSTROMS RESOLUTION AND THE COORDINATES DEPOSITED ARE THE FINAL 1.8 ANGSTROMS STRUCTURE WHICH IS BASICALLY THE SAME AS THAT AT 2.3 ANGSTROMS RESOLUTION. THERE ARE 8 D(C4) STRANDS PER ASYMMETRIC UNIT WHICH FORM TWO TETRAMERS. THE FIRST TETRAMER IS NUMBERED FROM 1 TO 16, AND THE OTHER TETRAMER FROM 17 TO 32. THERE ARE 46 WATER MOLECULES FOUND AT 1.8 A RESOLUTION. ALL HYDROGEN ATOMS ARE INCLUDED FOR EASY REFERENCE ALTHOUGH THEY ARE NOT REFINED WITH X-RAY DATA. THE STRUCTURE WAS SOLVED BY HEAVY ATOM PHASING. K2PTCL6 WAS SOAKED INTO THE CRYSTAL AND ONLY ONE PT SITE WAS FOUND WHICH WAS AT THE THREE-FOLD AXIS. SINGLE ISOMORPHOUS REPLACEMENT (SIR) PHASES AND SINGLE-WAVELENGTH ANOMALOUS SCATTERING (SAS) PHASES WERE IMPROVED BY SOLVENT FLATTENING. THE RESULTANT ELECTRON DENSITY MAP CLEARLY REVEALED THE INTERCALATED STRUCTURE FOR THE FIRST TIME.
U-DNA, QUADRUPLE HELIX, PARALLEL-STRANDED TETRAPLEX, BASE INTERCALATED, MISMATCHED, DNA