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Single-input module (SIM) was found in the E. coli transcriptional regulation network (Shen-Orr et al. 2002). A single transcription factor, X, regulates a set of operons Z1, …, Zn. X is usually autoregulatory. All regulations are of the same sign (positive or negative). No other transcription factor regulates the operons. Mathematical modeling suggests that SIM can show a detailed temporal program of expression resulting from differences in the activation thresholds of the different genes. Built into this design is a pattern in which the first gene activated is the last one to be deactivated. The SIM motif is found in systems of genes that function stoichiometrically to form a protein assembly (such as flagella) or a metabolic pathway (such as amino-acid biosynthesis).