Construction of a genetic switch for inducible trans-activation of gene expression in eucaryotic cells

The cotransfection of selectable marker genes and the gene for the nonstructural proteins NS1 and NS2 of the autonomous parvovirus H-1 failed to produce cell lines that constitutively expressed NS1. A plasmid, pP38NS1cat, was constructed that expressed the NS1-NS2 gene from the H-1 P38 coat protein promoter in place of the natural P4 promoter. The P38 promoter is constitutively weak and is trans-activated by NS1. Stable cell lines were isolated that contained pP38NS1cat that was constitutively silent, but inducible with exogenous NS1 by superinfection or by treatment with sodium butyrate. The cells that were induced for this self-stimulatory genetic circuit did not remain in the culture, suggesting that expression of NS1-NS2 is cytotoxic or that the expression is not sustained. The properties of these cell lines and an example of the construction of a cell line inducible for expression of the viral coat protein gene and the bacterial gene for chloramphenicol acetyltransferase (cat) are described.