DNA structure in which an adenine-cytosine mismatch pair forms an integral part of the double helix.
Extensive studies using one- and two-dimensional 1H NMR at 500 MHz revealed that the oligonucleotide d(CGCCGCAGC) in solution at 5 degrees C forms a double helix under conditions of high salt (500 mM in NaCl, 1 mM sodium phosphate), low pH (pH 4.5), and high DNA concentration (4 mM in duplex). The presence of very strong nuclear Overhauser effects (NOEs) from base H8/H6 to sugar H2',H2" and the absence of NOE from base H8/H6 to sugar H3' suggested that the oligomer under these solution conditions forms a right-handed B-DNA double helix. The following lines of experimental evidence were used to conclude that C4 and A7 form an integral part of the duplex: (i) the presence of a NOESY cross-peak involving H8 of A7 and H8 of G8, (ii) the presence of a two-dimensional NOE (NOESY) cross-peak between H6 of C3 and H6 of C4, (iii) base protons belonging to C4 and A7 forming a part of the H8/H6---H1' cross-connectivity route, and (iv) the pattern of H8/H6---H2',H2" NOESY cross-connectivity based upon a B-DNA model requiring that both C4 and A7 form an integral part of the duplex. The possibility of an A-C pair involving H bonds was also examined. Two possible structural models of the duplex at pH 4.5 are proposed: in one model A-C pairing involves two H bonds, and in the other A-C pairing involves a single H bond.
Institute of Biomolecular Stereodynamics, State University of New York at Albany 12222.
M H
MH
Sarma
G
G
Gupta
R H
RH
Sarma
R
R
Bald
U
U
Engelke
S L
SL
Oei
R
R
Gessner
V A
VA
Erdmann
D000241:Adenosine; D001482:Base Composition; D003596:Cytosine; D004247:DNA; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides
D009838:Oligodeoxyribonucleotides; D003596:Cytosine; D004247:DNA; D000241:Adenosine