Gene transfer by protoplast fusion: Expression cloning of rare gene products in mammalian cells

A method is described that facilitates performing a large number of protoplast fusions to mammalian cells simultaneously and successfully. This method makes it possible to circumvent typical hurdles to the use of transient expression in mammalian cells, facilitating expression cloning of DNA enoding the newly detected gene product of interest. The original in vitro assay used to define the new activity is of interest, adapted to microtiter plates, combined with protoplast fusion, extends the reach of expression cloning to such cases as products of a rare message, or activities involving a multisubunit or unstable protein or both.