J. Biol. Chem., Vol. 256, Issue 19, 9986-9989, 10, 1981
Carbon 13 spin-lattice relaxation, linewidth, and nuclear Overhauser enhancement measurements of nucleosome length DNA
GC Levy, PR Hilliard Jr, LF Levy, RL Rill and R Inners
Carbon 13 NMR data were obtained at four magnetic fields for double-
stranded DNA samples 120 and 160 nucleotide pairs long. Spectral linewidths
are several-fold smaller than predicted for overall rigid rod rotation and
increase with increasing field, indicating significant chemical shift
dispersion contributions to high field linewidths. Spin- lattice relaxation
times are short (e.g. T1 values for CH carbon atoms are approximately 0.5 s
at 67.9 MHz), and increase with increasing field. Nuclear Overhauser
effects of 0.6 to 0.8 (theoretical maximum = 2.0) were measured for the
same protonated carbon atoms at 100.6 MHz. These short T1 values nd
relatively large nuclear Overhauser effects show that double-stranded DNA
undergoes rapid internal motions with effective correlation times of a few
nanoseconds. Preliminary data indicate that DNA base carbon motions occur
on essentially the same time scale as sugar motions, thus arguing against
independent flexibility of the DNA backbone. Linewidths decreased 2- to
5-fold and nuclear Overhauser effects doubled, upon heat denaturation of
DNA, as expected for increased motion. On the other hand, NT1 values of
native and denatured DNA were nearly identical, suggesting insensitivity of
spin-lattice relaxation times to motions in the nanosecond range in these
relatively stiff chains.
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