Expression of a Bombyx cytoplasmic actin gene in cultured Drosophila cells: influence of 20-hydroxyecdysone and interference with expression of endogenous cytoplasmic actin genes.

The expression of the Bombyx cytoplasmic actin A3 gene and its response to 20-hydroxyecdysone are studied after transfection in hormone responsive Drosophila cells and are compared to the expression of homologous resident genes. The host cells accumulate correct transcripts of the Bombyx gene in a gene dosage dependent way. The relative amount of endogenous cytoplasmic actin mRNAs is decreased in transfected cells, whether the transgene is integrated into the genome or not. When 20-hydroxyecdysone is added to the culture medium, the accumulation of the foreign mRNA is decreased whereas those of endogenous cytoplasmic actin transcripts are increased. These results are discussed in terms of competition for transcription and regulatory factors.