Autoregulation at the level of mRNA 3′ end formation of the suppressor of forked gene of Drosophila melanogaster is conserved in Drosophila virilis

TheDrosophila melanogaster Suppressor of forked [Su(f)] protein shares homology with the yeast RNA14 protein and the 77-kDa subunit of human cleavage stimulation factor, which are proteins involved in mRNA 3′ end formation. This suggests a role for Su(f) in mRNA 3′ end formation inDrosophila . Thesu(f) gene produces three transcripts; two of them are polyadenylated at the end of the transcription unit, and one is a truncated transcript, polyadenylated in intron 4. Using temperature-sensitivesu(f) mutants, we show that accumulation of the truncated transcript requires wild-type Su(f) protein. This suggests that the Su(f) protein autoregulates negatively its accumulation by stimulating 3′ end formation of the truncatedsu(f) RNA. Cloning ofsu(f) fromDrosophila virilis and analysis of its RNA profile suggest thatsu(f) autoregulation is conserved in this species. Sequence comparison betweensu(f) from both species allows us to point out three conserved regions in intron 4 downstream of the truncated RNA poly(A) site. These conserved regions include the GU-rich downstream sequence involved in poly(A) site definition. Using transgenes truncated within intron 4, we show that sequence up to the conserved GU-rich domain is sufficient for production of the truncated RNA and for regulation of this production bysu(f) . Our results indicate a role ofsu(f) in the regulation of poly(A) site utilization and an important role of the GU-rich sequence for this regulation to occur.