Construction of the recombinant baculovirus via homologous recombination relies on the success of the co-transfection. OET offers a cost-effective approach to customers who wish to ensure success with their baculovirus co-transfection(s). For the co-transfection reaction, a transfer plasmid containing the gene of interest needs to be either provided by the customer or produced by OET. This transfer plasmid is then used with the flashBAC™ ULTRA baculoviral DNA to co-transfect insect cells (Sf9). A control co-transfection is also performed in which a transfer plasmid containing the lacZ gene is used. Following incubation of cells for five days at 28°C, the cell culture medium containing the recombinant virus is harvested. This virus stock (P0) is then sent to the customer.