This invention relates to the field of genetic engineering. Specifically, the invention relates to the construction of operons to produce biologically active agents. For example, operons may be constructed to produce agents that control the function of biochemical pathway proteins (e.g., protein phosphatases, kinases and/or proteases). Such agents may include inhibitors and modulators that may be used in studying or controlling phosphatase function associated with abnormalities in a phosphatase pathway or expression level. Fusion proteins, such as light activated protein phosphatases, may be genetically encoded and expressed as photoswitchable phosphatases. Systems are provided for use in controlling phosphatase function within living cells or in identifying small molecule inhibitors/activator/modulator molecules of protein phosphatases associated with cell signaling.