Transcription factor loading on the MMTV promoter: a bimodal mechanism for promoter activation.

The mouse mammary tumor virus (MMTV) promoter attains a phased array of six nucleosomes when introduced into rodent cells. This architecture excludes nuclear factor 1/CCAAT transcription factor (NF1/CTF) from the promoter before glucocorticoid treatment and hormone-dependent access of nucleolytic agents to promoter DNA. In contrast, when the promoter was transiently introduced into cells, NF1/CTF was bound constitutively and nucleolytic attack was hormone-independent. Thus, induction at this promoter was a bimodal process involving receptor-dependent remodeling of chromatin that allows NF1/CTF loading and direct receptor-mediated recruitment of additional transcription factors.