A peptide motif in Raver1 mediates splicing repression by interaction with the PTB RRM2 domain

Polypyrimidine tract-binding protein (PTB) is a regulatory splicing repressor. Raver1 acts as a PTB corepressor for splicing of alpha 3 tropomyosin (Tpm1) exon 3. Here we define a minimal region of Raver1 that acts as a repressor domain when recruited to RNA. A conserved [S/G][I/L]LGxxP motif is essential for splicing repressor activity and sufficient for interaction with PTB. An adjacent proline- rich region is also essential for repressor activity but not for PTB interaction. NMR analysis shows that LLGxxP peptides interact with a hydrophobic groove on the dorsal surface of the RRM2 domain of PTB, which constitutes part of the minimal repressor region of PTB. The requirement for the PTB-Raver1 interaction that we have characterized may serve to bring the additional repressor regions of both proteins into a configuration that allows them to synergistically effect exon skipping.