NUCLEOSOME PACKAGING AND NUCLEOSOME POSITIONING OF GENOMIC DNA

The goals of this study were to assess the extent to which bulk genomi c DNA sequences contribute to their own packaging in nucleosomes and t o reveal the relationship between nucleosome packaging and positioning , Using a competitive nucleosome reconstitution assay, we found that a t least 95% of bulk DNA sequences have an affinity for histone octamer in nucleosomes that is similar to that of randomly synthesized DNA; t hey contribute little to their own packaging at the level of individua l nucleosomes. An equation was developed that relates the measured fre e energy to the fractional occupancy of specific nucleosome positions, Evidently, the bulk of eukaryotic genomic DNA is also not evolved or constrained for significant sequence-directed nucleosome positioning a t the level of individual nucleosomes. Implications for gene regulatio n in vivo are discussed.