Abstract
Transcription factor (TF) signaling regulates gene transcription and requires a complex network of proteins. This network includes co-activators, co-repressors, multiple TFs, histone-modifying complexes, and the basal transcription machinery. It has been widely appreciated that pioneer factors, such as FoxA1 and GATA1, play an important role in opening closed chromatin regions, thereby allowing binding of a secondary factor. In this review we will focus on a newly proposed model wherein multiple TFs, such as steroid receptors (SRs), can function in a pioneering role. This model, termed dynamic assisted loading, integrates data from widely divergent methodologies, including genome wide ChIP-Seq, digital genomic footprinting, DHS-Seq, live cell protein dynamics, and biochemical studies of ATP-dependent remodeling complexes, to present a real time view of TF chromatin interactions. Under this view, many TFs can act as initiating factors for chromatin landscape programming. Furthermore, enhancer and promoter states are more accurately described as energy-dependent, non-equilibrium steady states.