Novel modes of splicing repression by PTB

Polypyrimidine-tract-binding protein (PTB) is a repressive regulator of alternative splicing. Models for PTB activity have ranged from simple binding competition with splicing factor U2AF(65) at regulated polypyrimidine tracts to looping out of repressed exons by binding of PTB to flanking sites. Structural analysis of PTB bound to RNA suggests how PTB monomers can induce loops, but two recent publications indicate that repression by PTB involves more than just binding to RNA.