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 respons e to 20-hydroxyecdysone are studied after transfection in hormone resp onsive Drosophila cells and are compared to the expression of homologo us resident genes. The host cells accumulate correct transcripts of th e Bombyx gene in a gene dosage dependent way. The relative amount of e ndogenous cytoplasmic actin mRNAs is decreased in transfected cells, w hether the transgene is integrated into the genome or not. When 20-hyd roxyecdysone is added to the culture medium, the accumulation of the f oreign mRNA is decreased whereas those of endogenous cytoplasmic actin transcripts are increased. These results are discussed in terms of co mpetition for transcription and regulatory factors.