The alpha subunit of human chorionic gonadotropin hormone synthesized in insect cells using a baculovirus vector is biologically active.

A recombinant baculovirus, vAc alpha hCG, having a replacement of the viral polyhedrin gene with the cDNA encoding the alpha subunit of hCG was used to express alpha hCG, an extensively glycosylated hormone, in insect cells. Virus-infected cells, 72 h pi, secreted approximately 11.3 micrograms alpha hCG/2 x 10(6) cells/ml which was identical to the native hormonal peptide in terms of electrophoretic mobility, immunoreactivity and bioactivity on association with beta subunit, as evident by its binding to rat testicular cells and induction of steroidogenesis in a mouse Leydig cell bioassay system. The alpha hCG secreted into the medium represented approximately 20-30% of the total hCG synthesized by vAc alpha CG infected insect cells. The implications of using a very late promoter, in a baculovirus expression system, for directing the transcription of a gene whose gene product requires extensive post-translational modifications are discussed.