Scheme of transfer plasmids for construction of recombinant baculoviruses.

The structure of the transfer plasmid was derived from pFastBac1. In all plasmids, Polh (polyhedron promoter of baculovirus) was used as a promoter of HERV env gene. As a polycistronic promoter, hEF1α was used for HPV16, 18, and 58L1 genes. For each plasmid, poly(A) (polyadenylation signal) was inserted at the end of each target gene. (A) pFB-HERV-HP16/18L1 was constructed by putting HPV 16L1 gene ahead of HPV 18L1. (B) pFB-HERV-HP18/16L1 was constructed by putting HPV 18L1 gene ahead of HPV 16L1. (C) pFB-HERV-HP16/18/58L1 was constructed by inserting HPV 58L1 gene between HPV 16L1 to HPV 18 L1 gene.