Selection of Intracellular Immunoglobulins

A method for determining the ability of antibody to bind to antigen in an intracellular environment comprises (a) providing first and second molecules which interact to generate a signal; (b) providing an intracellular antibody associated with the first molecule and an intracellular antigen associated with the second molecule; (c) assessing the intracellular Ab/Ag interaction by monitoring the signal generated; and, optionally, (d) isolating those antibodies which give rise to a signal. The antibody may be an intact immunoglobulin or a Fv, scFv, Fab or F(ab')<SB>2</SB> fragment. The first molecule may particularly be the activation domain of VP16 and the second molecule may be the binding domain of LexA