Interaction blues: protein interactions monitored in live mammalian cells by β-galactosidase complementation

In mammalian cells, protein–protein interactions constitute essential regulatory steps that modulate the activity of signalling pathways and many other intracellular processes. Although efficient genetic methods for identifying interacting partners exist and have been successfully applied by a number of laboratories, there has been a need for a technique that allows protein interactions to be monitored in real time in the cellular compartment in which they normally take place. The β-galactosidase-based intracistronic complementation methodology described here is the first technology that might fulfil these requirements and can be applied to live mammalian cells. In addition, it holds promise for applications in high-throughput screens for agonists and antagonists of specific interactions and for the development of a ‘mammalian two-hybrid’ screen for novel protein partners.