The structure of a DNA-RNA hybrid.

Secondary structure specificity of the nuclease activity of the 1,10-phenanthroline-copper complex.

“…The deoxyribose fragment generated by the presumed oxidative degradation has not yet been identified (15). In this communication, we report that the rate of cleavage of a poly(dT) strand that is complexed to a poly(rA) strand and therefore constrained to the A structure characteristic of RNA and RNADNA hybrids (16,17) is cleaved at a rate that is 10-20% of that observed with the Bhelical polymers poly(dA)-poly(dT) and poly(dA-dT). In addition, we report that poly(dG-dC) stabilized in the Z form by 3.0 M NaCl is resistant to cleavage, whereas the same polynucleotide in the B structure at lower salt concentrations is rapidly degraded.…”

“…Fiber x-ray diffraction analysis has shown that, unless a synthetic DNA is paired to a polyribonucleotide, it adopts an A-helix conformation only at very low humidity or in the complete absence of salt (3,23). However, DNA strands of the DNARNA hybrids are induced to form the A structure because the steric constraints associated with the 2'-hydroxyl group of the ribose prohibit the RNA strand from adopting a B form (16,17).…”

“…RESULTS A-DNA Cleavage. DNA-RNA heteroduplexes exhibit x-ray diffraction patterns and optical measurements characteristic of A helices (17,19,20) and provide convenient models of a DNA strand in that secondary structure in aqueous solution at physiological ionic strengths (21,22). Fiber x-ray diffraction analysis has shown that, unless a synthetic DNA is paired to a polyribonucleotide, it adopts an A-helix conformation only at very low humidity or in the complete absence of salt (3,23).…”

Filamentous bacterial viruses

“…An artificial complex of Ff DNA and complementary RNA has been studied by X-ray diffraction (131). The structure remains in a configuration similar to the A configuration of DNA under conditions which would transform A-DNA to B-DNA.…”

Structural and Energetic Considerations of Wave Propagation in DNA

“…Although our model predicts that double stranded RNA can undergo a conformational change from A RNA to 8 kinked RNA (so as to allow for drug intercalation) , the subsequent conversion of a kinked RNA to th.e B structure may not be possible for steric reasons. It is for thi.s reason that double stranded RNA and the RN~DNA hybrid helix exist solely as A structures (Langridge and Gomatos~ 1963;Milman et al,., 1967).…”