We isolated cDNA clones for the mouse orthologues of ten of the subunits [ PSMA 1 ( C 2 ) , PSMA 2 ( C 3 ) , PSMA 3 ( C 8 ) , PSMA 4 ( C 9 ) , PSMA 5 ( ZETA ) , PSMA 6 ( IOTA ) , PSMA 7 ( C 6 1 ) , PSMB 2 ( C 7 1 ) , PSMB 3 ( C 10 2 ) , and PSMB 5 ( 10 ) ] to complete the cloning of all of the mouse subunits . ^^^