Structure of the MFGS-p67^phox retroviral vector. The MFGS vector consists of the following parts from left to right in the figure: (A) a Mo-MuLV DNA fragment containing the 5′ LTR sequence; (B) the retroviral ψ-packaging sequence that contains splice donor (SD) and splice acceptor (SA) sites and residual gag sequence with extra stop codons; (C) the open reading frame of p67^phox, which was cloned into a unique Nco I site directly 3′ of the retroviral envelope ATG start codon; and (D) a Mo-MuLV 3′ long-terminal repeat (LTR).