Rbm9 is a RNA-binding protein that regulates alternative splicing events by binding to 5'-UGCAUGU-3' elements.Rbm9 prevents binding of U2AF2 to the 3'-splice site. Rbm9 regulates alternative splicing of tissue-specific exons and of differentially spliced exons during erythropoiesis. Rbm9 seems to act as a coregulatory factor of ER-alpha.