Supplementary Data are available at NAR Online.
The authors would like to thank Jonathan Widom for careful reading of the manuscript and many useful suggestions, and Eldon Emberly for providing experimental binding data for several TFs. A.V.M. would like to acknowledge a fellowship from the Leukemia and Lymphoma Society. J.J.H. is a fellow of the Jane Coffin Childs Memorial Fund for Medical Research. Funding to pay the Open Access publication charges for this article was provided by National Institutes of Health (NIH).
Conflict of interest statement. None declared.