UP-REGULATION OF THE DROSOPHILA-1731 RETROTRANSPOSON LONG-TERMINAL REPEAT BY UV-B IRRADIATION REQUIRES A SHORT SEQUENCE IN THE U3 REGION

A 1731 is a Drosophila melanogaster retrotransposon, the transcripts o f which decrease in Drosophila cells after treatment by the 20-hydroxy ecdysone (20-OH), the steroid-molting hormone of insects, In order to analyze the regulation of the long terminal repeat (LTR) directed tran scription by UV-B, S2 Drosophila cells were transfected with various c himeric constructs carrying the LTR of 1731 linked to the bacterial ch loramphenicol acetyltransferase (CAT) reporter gene and then subjected to UV-B irradiation, The results demonstrate that the 1731 LTR is act ivated by UV-B irradiation in a dose- and time-dependent manner, Using constructions expressing the reporter gene under the control of eithe r the entire or deleted LTRs of 1731, we established that a sequence l ocated in the U3 region was required for the retrotransposon to respon d to UV-B, The cis-acting element is identical to the binding sequence of the dorsal transcription factor, In addition, the S2 Drosophila ce ll produced extracellular factor(s) in response to UV-B irradiation wh ich activated the 1731 LTR in nonirradiated cells, This factor(s) was detected when responding cells were cocultured with inducing cells and when conditioned medium from irradiated cultures was added to the cel l cultures. (C) 1996 Academic Press, Inc.