Enhancer and silencer elements within the first intron mediate the transcriptional regulation of the β3 tubulin gene by 20-hydroxyecdysone in Drosphila Kc cells

Abstract We have studied the transcriptional regulation of the β 3 tubulin gene by the steroid hormone 20-hydroxyecdysone (20-E) in Drosophila Kc cells. A series of hydrid genes, with different fragments of the β 3 tubulin gene driving the bacterial chloramphenicol acetyl transferase (CAT) gene were constructed. The promoter activity was assayed after transient expression in Kc cells, in the presence and the absence of 20-E. Constructs with 0.91 kb upstream from the transcription start site and 360 bp from the first large intron allowed the hormonal regulation, i.e. a repression in the absence of 20-E and a derepression-activation in the presence of the hormone. This 360 bp fragment contains several enhancers and silencer(s) sequences. The regulation of the expression of the β 3 tubulin gene results from the combined activity of all the positive and negative regulatory sequences of the first intron, and a dialogue with the promoter sequences. The nucleotide sequence of this intronic regulatory-fragment has been established and we have identified several EcRE (ecdysone responsive element) consensus sequences.