Immediate-early baculovirus vectors for foreign gene expression in transformed or infected insect cells

Baculovirus expression vectors are used routinely for foreign gene expression and are under intense development as improved biological pesticides. Conventional baculovirus expression vectors are recombinant viruses that can express a foreign gene in insect cells under the control of the polyhedrin promoter, which provides high-level transcription during the very late phase of infection. For some applications, including foreign glycoprotein production and insect pest control, it might be advantageous to have baculovirus vectors that could express foreign gene products in uninfected cells or earlier after infection. To fulfill this need, we have constructed a new set of plasmids that can be used to clone and express foreign genes under the control of a baculovirus ie1 promoter, which is active in uninfected insect cells and throughout infection. We used a subset of these new plasmids to isolate recombinant baculoviruses containing various foreign genes and compared expression of these genes by the resulting immediate-early baculovirus vectors and by conventional baculovirus vectors. As expected, the immediate-early vectors began to express each foreign gene earlier in infection but, by 36-48 h postinfection, the conventional vectors had produced more of each foreign protein. Conventional baculovirus vectors also produced more enzymatic activity from two different procaryotic genes than the immediate-early baculovirus vectors. However, immediate-early vectors produced as much or more enzymatic activity from two different eucaryotic genes encoding secretory pathway proteins than the conventional vectors, even at 48 h postinfection. Hence, this report describes a new set of plasmids that can be used to clone and express foreign genes under the control of the baculovirus ie1 promoter and suggests that immediate-early baculovirus vectors might be as useful as conventional baculovirus expression vectors for producing biologically active eucaryotic secretory pathway proteins.