Identification of Novel Transmembrane Gene Sequence and Its Use for Cell-Surface Targeting of βSubunit of Human Chorionic Gonadotropin

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Abstract
We identified a 685-nucleotide gene fragment that codes for the transmembrane and cytoplasmic domains of glycoprotein of the LEP strain rabies virus and carried out experiments designed to express a novel fusion protein on the cell surface. The cDNA encoding the membrane anchor sequence was fused in the correct reading frame to the 3′ end of the cDNA encoding the β subunit of human chorionic gonadotropin (βhCG), a secretory glycoprotein that is used as an antigen for a contraceptive vaccine being developed in our laboratory. The fusion gene cassette was placed under the control of a vaccinia virus early promoter and cloned in a hostrestricted fowlpox viral vector. The recombinants, when used to infect mammalian cells that do not allow the replication of fowlpox virus, expressed the N-terminal 135 amino acid residues of βhCG anchored in the cell membrane by the 75-amino acid C-terminal sequence derived from rabies virus glycoprotein. This hybrid protein is correctly processed post-translationally and transported efficiently to the plasma membrane of nonpermissive cells such that the anchored βhCG molecule retains the correctly folded native antigenic epitope(s).