GAPDH and plasma cell myeloma: DTT treatment induced degradation of WT BLOC1S1 but not G444C BLOC1S1 in myeloma cells, as observed by a decrease in total BLOC1S1 and qTag expression in WT-transduced cells and an increase in BLOC1S1 and qTag expression relative to GAPDH in G444C-transduced cells (Fig. 6A).