Nucleic Acids Research, 1984, Vol. 12, No. 20 7793-7810
© 1984
Articles |
Synthesis and conformational studies of ribooligonucleotides which contain an alternating C-G sequence and show unusual circular dichroism spectra
Faculty of Pharmaceutical Sciences Suita Osaka 565, Japan *Institute for Protein Research, Osaka University Suita Osaka 565, Japan
Received August 17, 1984. Revised October 2, 1984. Accepted October 2, 1984.
The poly [r(C-G)]duplex shows an unusually large negative CD band in the long wavelength region. in order to elucidate this phenomenon, r(C-G-C-G) and r(C-G-C-G-C-G) were synthesized by a phosphotries method and their properties were examined by UV, CD, 1H and 31P NMR spectroscopy. These ribooligomers form self-duplexes at low temperature, the CD spectra of which show negative bands at around 290 nm and positive bands at around 265 nm. The of 1H nuclear Overhauser effect experiments, 1H chemical shift-temperature profiles of base protons, and the sharp singlet observed for all H1' protons are consistent with a normal A-RNA structure but not with, a Z-DNA like structure. The CD-temperature profiles and 31P NMR spectra support this conclusion. These results indicate that RNA duplexes with an alternating C-G sequence can give an unusually large negative CD band in the long wavelength region despite their right-handed helical structure.