Nucleic Acids Research, 1983, Vol. 11, No. 21 7517-7536
© 1983
CHEMISTRY |
Conformational analysis of m42C-m42C-m42A: a chemically modified 3'-acceptor end of tRNA, studied by NMR and CD methods
Gorlaeus Laboratories, Department of Chemistry, State University of Leiden P.O.Box 9502, 2300 RA Leiden, The Netherlands
Received October 3, 1983. Revised October 17, 1983. Accepted October 17, 1983.
A study on the conformation of the title compound, C-C-A, and on its constituent dinucleotides is presented. 1H-NMR spectra at 360 and 500 MHz were completely assigned by decoupling experiments. Computer simulation of the spectra yielded precise proton-proton and proton-phosphorus coupling constant values. The coupling constants are analyzed in terms of torsion angles and of N- and S-type sugar pucker.31P-NMR spectra gave some information about P-0 backbone torsion angles 
and 
. CD spectroscopy was used to obtain insight in the base-base interaction. The C(l) and C(2) unit in C-C-A show normal preference for N-type conformation of the sugar ring, whereas the A(3) residue appears rather biasecl towards the S-conformation The and a backbone torsion angles in the C-C phosphodiester linkage in C-C-A appear to assume normal g–, g– conformation, the , combination in the C-A linkage is proposed to have a g+, t conformation. In the C-C fragment in C-C-A a regular stack is indicated; it is suggested that the C-A part adopts an unusual anti-parallel base stack.