Abstract
Eukaryotic transcription factors (TF) function by binding to short 6-10 bp DNA recognition sites located near their target genes, which are scattered through vast genomes. Such process surmounts enormous specificity, efficiency and celerity challenges using a molecular mechanism that remains poorly understood. Combining biophysical experiments, theory and bioinformatics, we dissect the interplay between the DNA-binding domain of Engrailed, a Drosophila TF, and the regulatory regions of its target genes. We find that Engrailed binding affinity is strongly amplified by the DNA regions flanking the recognition site, which contain long tracts of degenerate recognition-site repeats. Such DNA organization operates as an antenna that attracts TF molecules in a promiscuous exchange among myriads of intermediate affinity binding sites. The antenna ensures a local TF supply, enables gene tracking and fine control of the target site’s basal occupancy. This mechanism illuminates puzzling gene expression data and suggests novel engineering strategies to control gene expression.
Highlights
Eukaryotic transcription factors (TF) function by binding to short 6-10 bp DNA recognition sites located near their target genes, which are scattered through vast genomes
As example of gene regulatory region (RR), we selected a fragment from the β3-tubulin gene, which is repressed by Engrailed[38]
We employed fluorescence correlation spectroscopy (FCS) as biophysical method to characterize the interactions between EngHD and the β3-tubulin regulatory regions (RR) in quasi-single particle conditions
Summary
Eukaryotic transcription factors (TF) function by binding to short 6-10 bp DNA recognition sites located near their target genes, which are scattered through vast genomes. Such process surmounts enormous specificity, efficiency and celerity challenges using a molecular mechanism that remains poorly understood. An interesting feature highlighted by genome analysis is an accumulation of potential TF binding sites in regions flanking eukaryotic genes[15] Such clusters of degenerate recognition sites are assumed to be key for transcription control[25], and are generally classified as gene regulatory regions (RR)[26]. When surrounding the target site, certain symmetric sequence repeats can affect the TF binding preference by simple statistical (or entropic) factors rather than by specific base recognition[27,28,29]
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