High level expression of nonfused foreign genes with Autographa californica nuclear polyhedrosis virus expression vectors.

High levels of nonfused chloramphenicol acetyltransferase, beta-galactosidase, and beta-glucuronidase expressed under the control of new vector constructs of the polyhedrin promoter in Spodoptera frugiperda cells infected with Autographa californica nuclear polyhedrosis virus were investigated by SDS-PAGE and RNA dot blot analysis of total cytoplasmic RNA. When the polyhedrin ATG start codon was converted to ATT by site-directed mutagenesis, translation initiated at downstream ATG codons resulting in high yields of nonfused foreign proteins. When a stop codon was inserted downstream from and in phase with the polyhedrin ATG codon but upstream from the ATG of a foreign gene, nonfused proteins were also produced, but at lower levels. The level of steady-state polyhedrin gene-promoted mRNA was not affected by the mutation from ATG to ATT or the insertion of in phase stop codons downstream from the polyhedrin ATG.