Nucleic Acids Research, 1980, Vol. 8, No. 3 643-656
© 1980
Articles |
Transfer RNA structure by carbon NMR: C2 of adenine, uracil and cytosine
+Oklahoma Medical Research Foundation and Department of Biochemistry and Molecular Biology, Oklahoma University Health Science Center Oklahoma City, OK 73104 *Division of Biological Sciences, University of Missouri Columbia, MO 65211, USA
Received September 27, 1979. Fourier transform 13C NMR spectra of E. coli tRNA enriched with 13C in either position 2 of adenine (60 atom % 13C) or in position 2 of uracil (82%) and cytosine (63%) were taken at 25.16 MHz over the temperature range 10°–76°. For C2 of adenine the peak was initially 5 ppm wide, but narrowed to 0.5 ppm as the molecule unfolded. C2 of uracil displayed behavior similar to that of adenine while the cytosine peak, initially relatively narrow at low temperature, sharpened less dramatically. Comparison of spectra at 26.16 MHz and 67.9 11Hz showed that the peak widths for folded tRNA were determined largely by chemical shift non-equivalence. T2 measurements suggested that intrinsic line widths of most cytosine C2 peaks were 4 Hz and 2–3 Hz for uracil. Adenine C2 with a directly bonded proton had resonances of about 40 Hz line width. T1 values were measured for C2 of adenine and the ribose carbons of tRNA. Consideration of dipolar relaxation and chemical shift anisotrophy led to a calculated rotational correlation time of 1.6±0.4x10–8 Sec for the adenines and 1.3±0.3x10–8 sec for tne ribose carbons.