a recombinant fusion protein is a protein created through genetic engineering of a fusion gene. this typically involves removing the stop codon from a cdna sequence coding for the first protein, then appending the cdna sequence of the second protein in frame through ligation or overlap extension pcr. that dna sequence will then be expressed by a cell as a single protein. the protein can be engineered to include the full sequence of both original proteins, or only a portion of either.