The borders ofcis-regulatory DNA sequences harbor the divergent transcription factor binding motifs in the human genome

Changes in the cis -regulatory DNA sequences and transcription factor (TF) repertoires provide major sources that shape the gene regulatory evolution in eukaryotes. However, it is currently unclear how dynamic change of DNA sequences introduce various divergence level of TF binding motifs in the genome over evolutionary time. Here, we estimated the evolutionary divergence level of the TF binding motifs, and quantified their occurrences in the DNase I hypersensitive sites. Results from our in silico motif scan and empirical TF-ChIP (chromatin immunoprecipitation) demonstrate that the divergent motifs tend to be introduced at the borders of the cis -regulatory regions, that are likely accompanied with the expansion through evolutionary time. Accordingly, we propose that an expansion by incorporating divergent motifs within the cis -regulatory regions provides a rationale for the evolutionary divergence of regulatory circuits.