X-IRRADIATION ACTIVATES THE DROSOPHILA-1731 RETROTRANSPOSON LTR AND STIMULATES SECRETION OF AN EXTRACELLULAR FACTOR THAT INDUCES THE 1731-LTR TRANSCRIPTION IN NONIRRADIATED CELLS

Using constructs expressing the reporter gene under the control of the entire or deleted long terminal repeats (LTRs) of 1731, a Drosophila melanogaster retrotransposable element, we show that 1731-LTR is activ ated by X-irradiation in a dose- and time-dependent manner, and that a sequence located in the U3 region of these LTRs is required, The cis- acting element conferring X-responsiveness shows similarities to kappa B (kappa B)-like binding sequence. In response to X-irradiation, S2 Dr osophila cells produced an extracellular factor which activates the 17 31-LTR in nonirradiated cells. This factor was detected both when tran sfected cells were cocultured with inducing cells and when a condition ed medium taken from irradiated cultures was added.