Consensus-binding sites for many transcription factors are relatively non-selective and
found at high frequency within the genome. This raises the possibility that factors that are
capable of binding to a cis-acting element in vitro and regulating transcription from a
transiently transfected plasmid, which would not have higher order chromatin structure, may
not occupy this site within the endogenous gene. Closed chromatin structure and
competition from another DNA-binding protein with similar nucleotide specificity are two …