A short 5' region of the long terminal repeat is required for regulation by hormone and heat shock of Drosophila retrotransposon 1731.

1731, a Drosophila retrotransposon was first described as having a transcription activity which was negatively regulated by 20-hydroxyecdysone (20-OH), the steroid molting hormone of insects. Using constructions expressing the bacterial chloramphenicol-acetyltransferase (CAT) gene under the control of the entire or deleted Long Terminal Repeats (LTRs) of 1731, we were able to show that a short (28 bp) sequence located in the U3 region of these LTRs was required for 1) the increase in promoter strength, 2) negative regulation by 20-OH and, 3) positive regulation by heat shock.