Cooperativity in gene expression is an important feature of many regulatory networks. Described using the Hill function, the most common example is a transcription factor (TF) that when bound to its target regulatory site, increases the rate of binding of other transcription factors (usually through TF-TF dimerization).
There are numerous example of TF dimerization-based cooperativity in the literature. However, I am trying to find examples of positive transcriptional cooperativity that involve mechanisms other than TF dimerization. In the dimer model, an unbound TF binds to its cognate promoter (containing multiple enhancers) with a certain affinity. With the first TF bound, another identical TF now has increased affinity for its target - binding to the enhancer and binding (dimerization) to the first TF. The expression profile is sigmoidal (near binary) and represents sharp on/off switching in activity.
Although peer-reviewed articles experimentally or theoretically characterizing alternative mechanisms are preferred, I'm also interested in user hypotheses and discussions that are more speculative. Specifically, I'm interested in positive cooperativity that occurs without feedback from the regulated genes.
One potential mechanism could involve a DNA-binding TF consisting of a transcriptional activator domain and a chromatin remodeling or DNA methylation domain. When the TF binds it not only activates transcription but remodels local chromatin. If the remodeling increases affinity for the next TF, they act cooperatively (and positively). Perhaps something similar to this has already been described.