Retrovirus-producing cells were constructed as described previously[13]. Briefly, PT67 packaging cells (Clontech) expressing the
Gibbon ape leukemia virus envelope gene were transiently transfected with pTet2-GWPT. The Tet2-GWPT viruses were subsequently harvested and added to GP2-293 cells (Clontech) that
expressed thegag andpolgenes of Moloney Murine Leukemia
Virus (MoMLV). were grown in the presence of hygromycin B
(150lg/ml) for 2 weeks and were transfected with pVSV-G (Clontech) to express VSV-G protein. Viruses were harvested 48 h posttransfection. Unless otherwise indicated, all cells were grown at
37C in a 5% CO2atmosphere in Dulbecco’s Modified Eagle’s Medium (DMEM) containing 4.5 g/l of glucose (GibcoBRL) and supplemented with fetal calf serum (10%), penicillin (100 U/ml),