Molecular dynamics and nuclear receptor function.

The development of live cell and biochemical analysis methods has led to an increase in our understanding of the dynamic regulation of transcription. Live single cell studies using photobleaching techniques indicate that many proteins have a high nuclear mobility. Pioneering work using promoter array systems based on the lac operon or the mouse mammary tumor virus promoter enabled the study of chromatin structure, promoter occupancy and protein-chromatin interaction dynamics in relation to transcription. Chromatin immunoprecipitation (ChIP)-based assays allow an exhaustive analysis of the temporal recruitment of proteins to an endogenous promoter and provide evidence of cyclic protein-protein and protein-promoter interactions. Although reflecting different timescales, both ChIP and live cell studies indicate a highly dynamic control of transcription that until now has gone undetected and unappreciated.