PSMB9 and overlapping connective tissue disease: To confirm that the elevated transcriptional activity is also translated into protein, PSMB8 and PSMB9 proteins were investigated in muscle tissue of representative patients with dermatomyositis (P2 and P3), polymyositis (P9), overlap syndrom (P16) and non-inflammatory muscle diseases (P18, P19, P20, P24).