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

A recombinant baculovirus, vAcα hCG, having a replacement of the viral polyhedrin gene with the cDNA encoding the α subunit of hCG was used to express αhCH, an extensively glycosylated hormone in insect cells. Virus-infected cells, 72 h pi, secreted ∼ 11.3 μg αhCG/2 × 10 4 cells/ml which was identical to the native hormonal peptide in terms of electrophoretic mobility, immunoreactivity and bioactivity on association with β subunit, as evident by its binding to rat testicular cells and induction of steroidogenesis in a mouse Leydig cell bioassay system. The αhCG secreted into the medium represented ∼20–30% of the total hCG synthesized by vAcα 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-translation modifications are discussed.