Fine tuning gene expression through short DNA-protein binding cycles

Certain transcription factors have recently been shown to interact with DNA in living cells, through very short binding cycles, contrasting with the data previously obtained in vitro, and with the view of a stepwise building of transcription initiation complexes. These short cycles are triggered by active dissociation mechanisms, suggesting that they ensure important biological functions. Various interpretations of these observations have been proposed, including a mechanism allowing the cell to switch off gene expression after removal of the inducer, or increasing the availability of free transcription factors. The interpretation examined here is that the brevity of the transcription factor turnovers favors the determinism of gene expression. For the genes with open chromatin and subject to this mode of interaction, the differential dynamics between promoter occupancy and the following processes mediating protein accumulation, can be essential for the dosage of gene expression. Biological activities and quantitative conditions allowing to increase the frequency of DNA-protein binding cycles are proposed. The unexpected dynamics of certain DNA-protein interactions can provide a concrete example of the notion of apparent gradation of single-site occupancy, which is a general solution allowing to extend the mass action determinism to low copy number molecules.