A model of how poly(dA:dT) tracts mediate extrinsic nucleosome-positioning effects. Illustrating a hypothetical role of poly(dA:dT) tracts in facilitating a the formation of an in vivo NFR during nucleosome assembly or remodeling. 5′ G:C-capped poly(dA:dT) tracts, in conjunction with downstream uncapped tracts, may guide the activity of a chromatin-remodeling complex or transcription factor. The 5′ capping residue may signal the initiation or termination of remodeling activity. This process may be coupled to the deposition of histone H2A.Z deposition into boundary nucleosomes. The NFR, once established, serves as the basis for subsequent transcriptional initiation events.
