Nonlinear Dynamics in Gene Regulation Promote Robustness and Evolvability of Gene Expression Levels
(a): The auto-activation circuit (circuit I) consists of a single gene, whose protein product (P) binds the promoter region to activate the expression of its own mRNA (M). The sink sign indicates mRNA and protein degradation/dilution. (b): A simple-activation circuit (circuit II) in which a transcription factor (purple) binds to the promoter region of a gene to activate the expression of mRNA (M). The protein product (P) is produced by translation of M. (c): A schematic representation of the G-P mapping. Genotypes are represented as discrete entities in the multi-dimensional parameter space of kinetic rates (indicated by the axes k1 → kn) and are mapped to their corresponding phenotypes, which are steady state solutions in the two-dimensional space spanned by M and P expression levels.