AUTOREGULATION AT THE LEVEL OF MESSENGER-RNA 3' END FORMATION OF THE SUPPRESSOR OF FORKED GENE OF DROSOPHILA-MELANOGASTER IS CONSERVED IN DROSOPHILA-VIRILIS

The Drosophila melanogaster Suppressor of forked [Su(f)] protein share s homology with the yeast RNA14 protein and the 77-kDa subunit of huma n cleavage stimulation factor, which are proteins involved in mRNA 3' end formation. This suggests a role for Su(f) in mRNA 3' end formation in Drosophila. The su(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 s ensitive su(f) mutants, we show that accumulation of the truncated tra nscript requires wild-type Su(f) protein. This suggests that the Su(f) protein autoregulates negatively its accumulation by stimulating 3' e nd formation of the truncated su(f) RNA. Cloning of su(f) from Drosoph ila virilis and analysis of its RNA profile suggest that su(f) autoreg ulation is conserved in this species. Sequence comparison between su(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) s ite definition. Using transgenes truncated within intron 4, we show th at sequence up to the conserved GU-rich domain is sufficient for produ ction of the truncated RNA and for regulation of this production by su (f). Our results indicate a role of su(f) in the regulation of poly(A) site utilization and an important role of the GU-rich sequence for th is regulation to occur.