RETROTRANSPOSON INSERTION INDUCES AN ISOZYME OF SN-GLYCEROL-3-PHOSPHATE DEHYDROGENASE IN DROSOPHILA-MELANOGASTER

The insertion of the blood retrotransposon into the untranslated regio n of exon 7 of the sn-glycerol-3-phosphate dehydrogenase-encoding gene (Gpdh) in Drosophila melanogaster induces a GPDH isozyme-GPDH-4-and a lters the pattern of expression of the three normal isozymes-GPDH-1 to GPDH-3. The process of transcript terminus formation inside the retro transposon insertion reduces the level of the Gpdh transcript that con tains exon 8 and increases the level of the transcript that contains e xons 1-7. The induced GPDH-4 isozyme is a translation product of the t hree transcripts that contain fragments of the blood retrotrapsposon. The mechanism of mutagenesis by the blood insertion is postulated to i nvolve the pause or termination of transcription within the blood sequ ence, which in turn is caused by the interference of a DNA-binding pro tein with the RNA polymerase. Thus, we show the formation of a new fun ctional GPDH protein by the insertion of a transposable element and di scuss the evolutionary significance of this phenomenon.