The immunoreactivities of the 5 representative mAbs with NusA-IRAS (10-120aa) were shown in Figure 2 , all of which specifically recognized a 78 kDa protein band which corresponded to the purified NusA-IRAS (10-120aa) protein, but not to the 66 kDa NusA protein. Anti-His mAbs reacted with both proteins in the same experiment (Figure 2(a) ) as controls. We evaluated the specificity of mAbs in mammalian cells by inserting IRAS cDNA into expression vectors to allow the production of GFP fusion proteins under the control of a CMV promoter. The pEGFPC1 and pEGFPC1-IRAS plasmids were separately transfected into HEK293 cells. Western blot analysis with the anti-GFP antibody demonstrated that chimeric proteins were expressed and migrated separately at expected molecular masses of approximately 19 or 27 KDa (Figure 2(b) ). However, the expected 190 kDa band whose molecular weight corresponded to the full-length IRAS protein was only detected with the mAbs DA041, DD015, and BE073 in GFP-IRAS expressed cells. The remaining BA022 and AH021 mAbs were negative (Figure 2(b) ). The same samples were also incubated with preimmune serum with no reactivity (data not shown). Results revealed that all 5 selected mAbs specifically recognized bacterially expressed NusA-IRAS (10-120aa) proteins, but only 3 mAbs recognized recombinant IRAS in mammalian cells.