RAPID, HIGH-LEVEL TRANSIENT EXPRESSION OF PAPILLOMAVIRUS-LIKE PARTICLES IN INSECT CELLS

Empirical scanning of natural or engineered peptide sequences for func tional residues is inherently dependent upon efficient is inherently d ependent upon efficient expression of large numbers of individual sequ ence variants to assay their relative functional potency. The insect b aculovirus system has been widely used for expression of viral coat pr oteins, but it generally requires prior isolation and expansion of a p lague-purified recombinant viral stock to generate useful quantities o f self-assembled virus-like particles. In search of a more rapid means of expression of analytical levels of the L1 coat protein of cotton-t ail rabbit and human type 11 papillomaviruses, we found that even brie f transient cotransfection of insect cells with baculovirus plasmid tr ansfer vectors and viral DNA yielded assembled particles that were imm unologically indistinguishable from particles obtained with plague-pur ified viral stocks. Within six days of plasmid/viral DNA cotransfectio n of Sf9 cells, at least 1-2 mu g of assembled L1 particles/100-mm pla te could be demonstrated, which proved more sufficient to assay functi onality. Transient cotransfection of insect cells should provide gener al utility for rapid high-level expression of sets of protein sequence variants, as well as other sequence-scanning applications such as seq uence optimization in protein engineering.