Androgen receptor complexes probe DNA for recognition sequences by short random interactions

Abstract

Due to the tremendous progress in microscopic imaging of fluorescently labeled proteins in living cells, the insight into the highly dynamic behavior of transcription factors has rapidly increased over the past decade. However, a consistent quantitative scheme of their action is still lacking. Using the androgen receptor as a model system, we combined three different fluorescence microscopy assays: single-molecule microscopy, photobleaching and correlation spectroscopy, to provide a quantitative model of the action of this transcription factor. This approach enabled us to distinguish two types of AR-DNA binding: very brief interactions, in the order of a few hundred milliseconds, and hormone-induced longer-lasting interactions, with a characteristic binding time of several seconds. In addition, freely mobile ARs were slowed down in the presence of hormone, suggesting the formation of large AR-coregulator complexes in the nucleoplasm upon hormone activation. Our data suggest a model in which mobile, hormone-induced transcription factor-coregulator complexes probe DNA by briefly binding at random sites, and only forming relatively stable transcription initiation complexes when bound to specific recognition sequences.