The cell is an extremely complex network of interactions between large numbers of molecules. Understanding this entire network and the information arising from it is an overwhelming and challenging task. Reverse genetics has given us the possibility to discover unknown interactions and their related pathways. With the help of peptide libraries, interactions between biomolecules can be disrupted or distorted and the signaling pathways where these proteins are involved, altered. Consequently, novel biological pathways can be discerned. The peptide libraries become a pool of shapes, some of them might behave as dominant effectors. With the use of retroviral transfer vectors those libraries can be expressed in a stable manner in the mammalian cell. A strong selection and screening process can finally lead to specific peptides. Novel high-throughput approaches might allow for the rapid creation of small-molecule switches in protein-protein interactions. Reverse genetics and as such the expression of small molecules that will have a specific biological outcome, can become an answer to our queries.