Figure 5.

Model of accessibility. (A) Transiently introduced recombination substrate not packaged into nucleosomes is recombinationally and transcriptionally active. (B) Stably maintained, nucleosomal targets are refractory to recombination and transcription. (C) Steroid-dependent glucocorticoid receptor binding to the MMTV LTR disrupts nucleosome activating recombination but not transcription. (D) Disruption of the nucleosomes allows assembly of transcription factors and coactivators, allowing transcriptional transactivation and presumably recombination. E1a can block the transition from C to D by preventing p300 assembly on the promoter.