Creating conditional mutations in mammals.

For many years geneticists have relied on conditional activation to study the roles of cytolytic or cytostatic proteins in lower eukaryotes or to elucidate the epistatic relationships of proteins in a signaling pathway. Regardless of their merits, conditional mutants have only been available to mammalian geneticists within the past few years. Moreover, the approaches that exist are still limited to a subset of signaling molecules and are not reliable for in vivo studies. Now, added to the biologist's toolbox is a versatile new approach based on chemically induced dimerization that should allow for the reversible regulation of proteins at the cell surface, intracellularly, in the nucleus and in vivo.