20-Hydroxyecdysone induces the expression of one beta-tubulin gene in Drosophila Kc cells

The expression of 56D and 60C beta-tubulin genes has been examined in Drosophila melanogaster Kc cells in response to the insect moulting hormone, 20-hydroxyecdysone (20-OH-E). Northern blots probed with beta-tubulin subclones show that the 56D beta-tubulin gene encodes a 1.8 kb mRNA whose abundance is not affected by 20-OH-E. The 60C gene probe detects two mRNAs: one of 1.8 kb present in untreated and 20-OH-E-treated cells, and one of 2.6 kb present only in 20-OH-E-treated cells; using a 60C 3'-specific probe, only the 2.6 kb is revealed. Hybrid selection translation experiment demonstrates that a 20-OH-E-inducible mRNA homologous to the 60C gene encodes a beta-tubulin subunit (P4); this subunit is the so-called beta 3-tubulin. Translation of size-fractionated mRNA shows that the 20-OH-E-induced beta 3-tubulin subunit is encoded, in treated cells, by the 2.6 kb mRNA.