| We report here identification and functional characterization of a new splicing factor , Sip 1 ( SC 35 interacting protein 1 ) . ^^^ Sip 1 was initially identified by virtue of its interaction with SC 35 , a splicing factor of the SR family . ^^^ Purified recombinant Sip 1 protein , but not other RS domain containing proteins such as SC 35 , ASF / SF2 , and U2AF65 , restored the splicing activity of the Sip 1 immunodepleted extract . ^^^ |