The gypsy retroposon of Drosophila melanogaster contains a sequence that potentiates upstream polyadenylylation sites. In contrast to other sequences that influence poly(A) site use, it appears to operate at the level of the DNA template. Nuclear extracts contained protein that bound to a repeated motif in the DNA. Flies with mutations that reduced transcripts polyadenylylated in the 5' long terminal repeat of gypsy contained less DNA-binding activity than wild type. A change in the repeat motif reduced both protein binding and poly(A) site potentiation. These findings provide evidence that DNA-binding proteins can regulate polyadenylylation sites.
