Mini Symposium

Qualitative statements about the regulation of gene activity often contain phrases such as "both transcription factor A and transcription factor B are required for the full activation of gene G, but compound C represses its expression". Such assertions are reminiscent of statements in Boolean logic, in this case: G = A and B and not C. In the absence of quantitative mechanistic information, modelers of gene regulation often revert to using similar Boolean expressions (or their set-theoretical equivalents), to describe the interaction of enhancers, repressors, and other trans-regulatory factors, and to perform semi-quantitative calculations to predict network responses. I will discuss the pros and cons of the Boolean approach in the light of the fact that only when certain unrealistic assumptions are made about transcription factor interaction, such approximations can validly replace a 'traditional' approach based on thermodynamic considerations.