Abstract
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.
Highlights
Carbon 13 NMR data were obtainedat four magnetic al. have reported protonatedsugarandbasecarbon fieldsfordouble-stranded DNA samples 120and160 relaxationbehaviorand NOE values at 25 M H z [6]
Carbon 13 spectra of 120 np length, fully double-stranded DNA fragmentswereobtained at four magnetic fields, the highest being 100.6 MHz (Fig.1).All observedlinewidthswere significantly smallerthan those calculated from overall rotational correlation times for a rigid rod corresponding to this DNA length
Onlythe linewidthsdetermined at the lower fields appear to be controlled strictly by dynamics (Fig. 2)
Summary
9986-9989, 1981 Printed in U.S.A. Carbon 13 Spin-Lattice Relaxation, Linewidth, and Nuclear Overhauser Enhancement Measurementsof Nucleosome LengthDNA*. Carbon 13 NMR data were obtainedat four magnetic al. Spectral linewidths areseveral- relatively narrow spectralilnes observed in spectra of all three fold smaller than predicted for overall rigid rod rota- nuclei, and significant magnitude of these early NOE meastion and increase with increasing field, indicatingsig- urements, cannot be interpreted in terms of the rotational nificant chemicalshift dispersion contributionsto high correlation times of reasonable rigid rod models We reported 13C spectra of hauser effects doubled, uponheat denaturationof DNA, native andheat-denatured, nucleosome core length NT1values of native and denatured DNA were nearly describe in more detail multifield I3C data on double- and identical, suggesting insensitivity of spin-latticerelax- single-stranded,near nucleosome corelength (120 and 160 np) ation timesto motions in the nanosecond rangein these DNA. Nuclear Overhauser enhancements of individual sugar and certain base carbonatoms at 100.6 MHz, andthree lower frequencies
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