We have constructed expression vectors for streptavidin-containing chimeric proteins. These vectors- carry the DNA sequence corresponding to the core region of the streptavidin molecule, and have several unique cloning sites which facilitate construction of gene fusions of streptavidin with a target protein. A chimeric protein of streptavidin and the target protein should be expressible in Escherichia coli by using the T7 expression system. Because of the strong and specific biotin-binding affinity of the streptavidin moiety, such streptavidincontaining chimeric proteins should extensively expand the applications of the streptavidin-biotin system, and offer a variety of applications as new biological tools.