| Here we demonstrate that PSMC 1 , an ATPase like subunit of the 19 S proteasome component , also interacts with HBX and PSMA 7 . ^^^ Analysis of the interacting domains among PSMA 7 , PSMC 1 , and HBX by deletion and site directed mutagenesis suggested a mutually competitive structural relationship among these polypeptides . ^^^ The crucial HBX sequences involved in interaction with PSMA 7 and PSMC 1 are important for its function as a transcriptional coactivator . ^^^ |