Improve the System A "systems biology" approach may clarify, for example, how particular proteins determine sensitivity of bacteria to extremes of temperature. Chang et al. (p. 1220) integrated information on protein structure with a model of metabolism, thus associating the protein structure of enzymes with their catalyzed metabolic reactions. The effects of temperature on susceptible proteins could be predicted and the key reactions that were likely to mediate sensitivity of bacteria to extremes of temperature were identified. Indeed, engineered thermotolerant proteins could be substituted for sensitive ones to improve the growth of thermosensitive strains of bacteria. Such control could come in handy when engineering strains of bacteria to produce compounds of industrial or therapeutic value.