Proper spatiotemporal gene expression is achieved by selective DNA binding of transcription factors in the genome. The most intriguing question is how dynamic interactions between transcription factors and their target sites contribute to gene regulation by recruiting the basal transcriptional machinery. Here we demonstrate individual binding and dissociation events of the transcription factor cAMP response element-binding protein (CREB), both in vitro and in living cells, using single-molecule imaging. Fluorescent-tagged CREB bound to its target sequence cAMP-response element (CRE) for a remarkably longer period (dissociation rate constant: 0.21s -1) than to an unrelated sequence (2.74s -1). Moreover, CREB resided at restricted positions in the living cell nucleus for a comparable period. These results suggest that CREB stimulates transcription by binding transiently to CRE in the time range of several seconds.
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