THE SPLICING FACTOR SRP20 MODIFIES SPLICING OF ITS OWN MESSENGER-RNA AND ASF SF2 ANTAGONIZES THIS REGULATION/

SRp20 is a member of the highly conserved SR family of splicing regula tors. Using a variety of reporter gene constructs, we show that SRp20 regulates alternative splicing of its own mRNA. Overexpression of SRp2 0 results in a reduction in the level of exon it-skipped SRp20 transcr ipts and activates the production of transcripts containing exon 4. Th ese exon 4-included transcripts encode a truncated protein lacking the C-terminal RS domain. We provide evidence that SRp20 probably enhance s the recognition of the otherwise unused, weak splice acceptor of exo n 4. The recognition of exons with weak splice acceptor sites may be a general activity of SRp20. Unexpectedly, ASF/SF2, another member of t he SR family, antagonizes the effect of SRp20 on SRp20 pre-mRNA splici ng and suppresses the production of the exon 4-included form. Our resu lts indicate that ASF/SF2 suppresses the use of the alternative exon 4 , most likely by inhibiting the recognition of the splice donor of exo n 4. These results demonstrate, for the first time, an auto-regulatory activity of an SR protein which is antagonized by a second SR protein .