Fig. 5.

Retrotransposition occurs in G₁/S-arrested but not in G₀ cells. (a) Retrotransposition in stationary cells infected with A/RT virus. Actively dividing (1), G₁/S-arrested (2), and G₀ phase (3) Gli36 cells infected with A/RT virus at a moi of 10 were prepared as described in Materials and Methods, and after confirmation of cell cycle status by FACS and adenovirus infection efficiency by β-gal, the cells were analyzed for expression of EGFP. In parallel control experiments, actively dividing, G₁/S-arrested, and G₀ phase cells also were infected with either HIV-based self-inactivating lentivirus vector (HIV) or replication-competent retrovirus (MLV) and also were analyzed for EGFP expression. nt, not tested. Data are representative of three independent experiments, all yielding similar results. (b) A/RT retrotransposition does not occur in G₀ phase cells. G₀ phase cells were infected with the A/RT virus at a moi of 10 and maintained in the nondividing state without passaging (G₀ phase) for 5 days. At 5 days after infection, cell cycle status and expression of β-gal and EGFP were examined as above. A parallel set of cells infected as above were then passaged and allowed to resume cell division (cycling resumed) and analyzed 7 days later.