Expression of heat shock-β-galactosidase hybrid genes in cultured Drosophila cells

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Abstract
Derivatives of Drosophila 70,000 dalton heat shock protein (hsp70) genes were constructed in which all of the hsp70 coding sequence but for the first seven codons had been substituted by a DNA segment coding for E. coli β-galactosidase. The constructs were capable of directing the synthesis of active β-galactosidase in COS1 (SV40 transformed African Green Monkey Kidney) cells. The hybrid genes were then used to develop a procedure permitting the introduction of genes and their transient expression in cultured cells of Drosophila melanogaster. Introduction of hybrid genes was achieved by DEAE-dextran-mediated transfection. Substantial gene activity was observed in heat-treated cells only 4 h, maximal activity 24 h after transfection. Various parameters of the transfection/transient expression system including the effects of different 3'nontranslated sequences on hybrid gene expression were investigated in an attempt to provide a useful procedure for studies of the expression of other genes in D. melanogaster cells. To show that promoters which are weaker than that of the hsp70 gene direct the synthesis of easily measurable amounts of β-galactosidase in D. melanogaster cells, the expression of a hsp84-β-galactosidase hybrid gene was also examined. Expression of the hsp70 hybrid gene occurs during heat shock, at temperatures at which other proteins are not made, and decreases sharply after heat treatment. The expression of the transfected gene therefore closely follows that of the endogenous hsp70 genes. This result suggests that a short hsp70 gene segment consisting of 195 base pairs of upstream sequence and a complete RNA leader region contain all the information required for the induced synthesis of proteins during heat shock.