Two mammalian introns, the human growth hormone intron and the Simian virus 40 large T antigen intron, were inserted into the coding sequences of diphtheria toxin fragment A (DT-A) and barnase (Bar), respectively, to disrupt their open-reading frames (ORFs). Expression of these two toxic proteins were totally abolished, which enabled the production of normal levels of recombinant baculoviral an...