A streptavidin-protein A chimera that allows one-step production of a variety of specific antibody conjugates.

We have expressed a gene fusion of streptavidin and the two immunoglobulin G (IgG)-binding domains of protein A in Escherichia coli. The purified chimeric protein had full biotin-binding ability, and bound one IgG molecule per subunit (31.4 kD). The affinity of the chimeric protein both for biotin and IgG can be used to provide antibody molecules with additional recognition capabilities. For example, the chimera will allow any IgG molecule to be used for sensitive biotin-linked detection systems without the need for chemical modification.