| Use of the yeast two hybrid system to identify proteins that associate with ST 7 ' s cytoplasmic domain revealed that this domain interacts with three proteins involved in signal transduction and / or endocytosis , viz . , receptor for activated protein C kinase 1 ( RACK 1 ) , muscle integrin binding protein ( MIBP ) , and SMAD anchor for receptor activation ( SARA ) , suggesting that ST 7 , like other proteins in the LDLR superfamily , functions in these two pathways . ^^^ |