Intracellular antibodies

A method for determining the ability of a immunoglobulin single domain to bind to a target in an intracellular environment, the method comprising the steps of:

• a) providing a first molecule and a second molecule, wherein stable interaction of the first and second molecules leads to the generation of a signal;
• b) providing an intracellular immunoglobulin single domain which is associated with the first molecule, said immunoglobulin single domain being free of a complementary immunoglobulin domain, and wherein the immunoglobulin single domain comprises a VH domain having at least 95% identity to the consensus sequence of SEQ ID No 3;
• c) providing an intracellular target which is associated with the second molecule, such that binding of the immunoglobulin single domain and the target leads to stable interaction of the first and second molecules and generation of the signal;
• d) determining the binding between the immunoglobulin single domain and the target by monitoring the signal.