The SIM network motif is a simple pattern in which one regulator controls a group of genes. Despite its simple structure, the SIM has an interesting dynamical function: it can generate temporal programs of expression, in which genes are turned on one by one in a defined order. In Escherichia coli, these temporal programs are found to match the functional order of the gene products. This is a “just-when-needed” production strategy, not making a protein before it is needed. Such a strategy is optimal for rapid production of a system made of diἀerent types of proteins, under constraints of limited resources for producing these proteins.