J. Dworkin et al., A PROTEIN-INDUCED DNA BEND INCREASES THE SPECIFICITY OF A PROKARYOTICENHANCER-BINDING PROTEIN, Genes & development, 12(6), 1998, pp. 894-900
Control of transcription in prokaryotes often involves direct contact
of regulatory proteins with RNA polymerase from binding sites located
adjacent to the target promoter. Alternatively, in the case of genes t
ranscribed by Escherichia coli RNA polymerase holoenzyme containing th
e alternate sigma factor sigma(54), regulatory proteins bound at more
distally located enhancer sites can activate transcription via DNA loo
ping by taking advantage of the increasing flexibility of DNA over lon
ger distances. While this second mechanism offers a greater possible f
lexibility in the location of these binding sites, it is not clear how
the specificity offered by the proximity of the regulatory protein an
d the polymerase intrinsic to the first mechanism is maintained. Here
we demonstrate that integration host factor (IHF), a protein that indu
ces a sharp bend in DNA, acts both to inhibit DNA-looping-dependent tr
anscriptional activation by an inappropriate enhancer-binding protein
and to facilitate similar activation by an appropriate enhancer-bindin
g protein. These opposite effects have the consequence of increasing t
he specificity of activation of a promoter that is susceptible to regu
lation by proteins bound to a distal site.