Solution structure of an RNA.2'-O-methylated RNA hybrid duplex containing an RNA.DNA hybrid segment at the center.

The solution structure of an RNA.2'-O-methylated RNA hybrid duplex containing an RNA.DNA hybrid segment at its center, (ggagaugac).(GmUmCmATCTCmCm), where lowercase letters, capital letters, and capital letters with the subscript m are RNA, DNA, and 2'-O-methylated RNA residues, respectively, was determined by observing the NMR spectra and performing the full relaxation matrix refinement. The 2'-O-methylation gives several characteristic features to oligoribonucleotides. In addition, this hybrid duplex is cleaved at a specific position by Escherichia coli ribonuclease HI, and so the role of the tertiary structure during the substrate recognition by the enzyme is of interest. The NOE connectivities among the proton resonances revealed that the duplex was a right handed helix. The 2'-O-methylated RNA segments had a typical C3'-endo conformation, and the 2'-O-methyl groups were directed to the minor groove of this duplex, taking the torsion angles phi (C1'-C2'-02'-CH3) that were all gauche(+). The DNA residues in the central RNA.DNA hybrid duplex formed the C3'-endo conformation, except for the middle thymine residue. No remarkable structural discontinuities were observed around the junction sites at either the 5'- or 3'-end of the DNA. The overall structure was close to the typical A-form duplex.