Design of Repressible Gene Circuits: M.E. Wall et al. 1 Design Principles for Regulator Gene Expression in a Repressible Gene Circuit Michael E. Wall1,2, William S. Hlavacek3* and Michael A. Savageau4+ 1Computer and Computational Sciences Division and 2Bioscience Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA 3Theoretical Biology and Biophysics Group (T-10), Theoretical Division, Mail Stop K710, Los Alamos National Laboratory, Los Alamos, NM 87545, USA 4Department of Microbiology and Immunology, The University of Michigan Medical School, Ann Arbor, MI 48109-0620, USA +Current address: Department of Biomedical Engineering, One Shields Avenue, University of California, Davis, CA 95616, USA. *Corresponding author Tel.: +1-505 665 1355 Fax: +1-505 665 3493 E-mail address of the corresponding author:
[email protected] Design of Repressible Gene Circuits: M.E. Wall et al. 2 Summary We consider the design of a type of repressible gene circuit that is common in bacteria. In this type of circuit, a regulator protein acts to coordinately repress the expression of effector genes when a signal molecule with which it interacts is present. The regulator protein can also independently influence the expression of its own gene, such that regulator gene expression is repressible (like effector genes), constitutive, or inducible. Thus, a signal-directed change in the activity of the regulator protein can result in one of three patterns of coupled regulator and effector gene expression: direct coupling, in which regulator and effector gene expression change in the same direction; uncoupling, in which regulator gene expression remains constant while effector gene expression changes; or inverse coupling, in which regulator and effector gene expression change in opposite directions.