Identification of the LUDSN provirus and expression of the transgene in HEP LB cells. Cells were infected with LUDSN7, LUDSN11, and LUDSN16 by centrifugation in the retroviral supernatant at 1,000g and selected for 3 weeks with G418 (see Materials and Methods). (A) Provirus integration into the genomic DNA of LB deficient cells (Southern blot analysis). Ten micrograms of genomic DNA extracted from transduced and selected LB45/LUDSN7, LB45/LUDSN11, and LB45/LUDSN16 cell lines was digested with Sac I, blotted, and probed with the 1.2-kb human UROD cDNA. Lane 0, 10 μg of DNA from untransduced LB cells. Lanes 2 and 10 contained plasmid DNA (20 and 100 pg, respectively) mixed with 10 μg of noninfected DNA corresponding to 2 and 10 copies per cell. The 3.0-kb band corresponds to the integrated provirus and the 6.5-kb band corresponds to the endogenous UROD gene. Note that the migration of the 3.0-kb band for LB45 samples were artefactually sligthly different from the control plasmid DNA. (B) UROD activity in transduced and deficient LB45 cell lines. Values are the means ± SD of three to six determinations.** P < .01v noninfected LB45 cells.