Proc Natl Acad Sci U S A. 2005 May 31;102(22):7841-6. doi:10.1073/pnas.0500365102

Balázsi G, Barabási AL, Oltvai ZN.

Topological units of environmental signal processing in the transcriptional regulatory network of Escherichia coli.

Defines origons as subnetworks originating from a single TF (in their model - a directed regulatory network - there is no strong component).