Expression vectors encoding bispecific fusion proteins and methods of producing biologically active bispecific fusion proteins in a mammalian cell

An expression vector encoding a functional bispecific fusion protein comprising a single recombinant bispecific single chain cassette comprising (1) a DNA sequence encoding a first antibody binding domain having two variable regions capable of binding a target, (2) a DNA sequence encoding a second antibody binding domain having two variable regions which bind a target, wherein each domain binds to a different target, and (3) a hydrophilic linker encoding a helical peptide comprising charged amino acids which links the DNA sequence encoding the first binding domain and the DNA sequence encoding the second binding domain.