Nucleosome core particles containing a poly(dA•dT) sequence element exhibit a locally distorted DNA structure

Poly(dA.dT) DNA sequence elements are thought to promote transcription by either excluding nucleosomes or by altering their structural or dynamic properties. Here, the stability and structure of a defined nucleosome core particle containing a 16 base-pair poly(dA.dT) element (A(16) NCP) was investigated. The A(16) NCP requires a significantly higher temperature for histone octamer sliding in vitro compared to comparable nucleosomes that do not contain a poly(dA-dT) element. Fluorescence resonance energy transfer showed that the interactions between the nucleosomal DNA ends and the histone octamer were destabilized in A(16) NCP. The crystal structure of A(16) NCP was determined to a resolution of 3.2 A. The overall structure was maintained except for local deviations in DNA conformation. These results are consistent with previous in vivo and in vitro observations that poly(dA-dT) elements cause only modest changes in DNA accessibility and modest increases in steady-state transcription levels. (c) 2006 Elsevier Ltd. All rights reserved.