Method for identifying validated target and assay combinations for drug development

The invention comprises methods useful within a larger process for identifying compounds and/or designing further compounds with activity to produce a desired phenotype (for example, growth inhibition) in cells whose target cell component is the subject of certain studies to identify such compounds. The invention employs constructed cells comprising a regulable gene encoding a biomolecule which modulates (inhibits or activates) in vivo the function of a target component of the cell which can be an enzyme, for example, methionyl-tRNA synthetase of Staphylococcus aureus . The process incorporates methods for identifying biomolecules that bind to a chosen target cell component in vitro, methods for identifying biomolecules that also bind to the chosen target and modulate its function intracellularly, causing a phenotypic effect. The intracellular effect of a biomolecule can be tested in cell culture, or tested after introduction of the constructed cells into a host mammal in vivo, and methods for identifying compounds that compete with the biomolecules for sites on the target in competitive binding assays. Compounds identified by the series of steps in this process are candidates for drugs with the desired activity on the cell. Targets for which such compounds can be identified are validated as being essential to a phenotype of the cell.