Global structure and mechanical properties of a 10-bp nucleosome positioning motif

The method of DNA cyclization kinetics reveals special properties of the TA TAAACGCC sequence motif found in DNA sequences that have high affinity for core histones. Replacement of 30 bp of generic DNA by th ree 10-bp repeats of the motif in smalt cyclization constructs increases cyclization rates by two orders of magnitude. We document a 13 degrees bend in the motif and ch aracterize the direction of curvature. The bending force constant is smalle r by nearly 2-fold and there is a 35% decrease in the twist modulus, relati ve to generic DNA. These features are the likely source of the high affinit y far bending around core histones to farm nucleosomes. Our results establi sh a protocol for determination of the ensemble-averaged global solution st ructure and mechanical properties of any approximate to 10-bp DNA sequence element of interest, providing information complementary to that from NMR a nd crystallographic structural studies.