Structure of an RNA internal loop consisting of tandem C-A+ base pairs.
The crystal structure of the RNA octamer 5'-CGC(CA)GCG-3' has been determined from X-ray diffraction data to 2.3 A resolution. In the crystal, this oligomer forms a self-complementary double helix in the asymmetric unit. Tandem non-Watson-Crick C-A and A-C base pairs comprise an internal loop in the middle of the duplex, which is incorporated with little distortion of the A-form double helix. From the geometry of the C-A base pairs, it is inferred that the adenosine imino group is protonated and donates a hydrogen bond to the carbonyl group of the cytosine. The wobble geometry of the C-A+ base pairs is very similar to that of the common U-G non-Watson-Crick pair.
Structural Biology Department, Physical Biosciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley 94720, USA.
S B
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Jang
L W
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Hung
Y I
YI
Chi
E L
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Holbrook
R J
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Carter
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Holbrook
D000225:Adenine / Q000737:chemistry*; D001482:Base Composition; D018360:Crystallography, X-Ray; D003596:Cytosine / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009843:Oligoribonucleotides / Q000737:chemistry; D012313:RNA / Q000737:chemistry*; D013816:Thermodynamics
D009843:Oligoribonucleotides; D012313:RNA; D003596:Cytosine; D000225:Adenine