Figure 2. Forkhead box A1 (FoxA1) is a pioneer factor belonging to a special class of proteins that are able to interact directly with condensed chromatin prior to any other transcription factors.

Upon chromatin binding, FoxA1 induces a nucleosomal rearrangement that results in a more relaxed chromatin structure, which is accessible to other transcription regulators, including ERs. Green diamonds represent epigenetic histone modifications (dimethylation of histone H3 at lysine 4, H3K4me2).