Characterization of the aMFG-EGFP retroviral producer cell line. (A) Schematic representation of the MFG-EGFP retroviral vector. LTR, long terminal repeat; ψ, viral packaging signal; SD and SA, splice donor and acceptor sites, respectively; gag and env indicate the presence of part of the MoMLV gag and env sequences. The predicted sizes of the two expected RNA isoforms are indicated. (B) FACS analysis of EGFP expression; the corresponding profile of the packaging cell line GP+envAm12 (thin line) is overlaid for comparison. (C) Northern blot analysis of aMFG-EGFP RNA. Total RNA (25 μg) from producer cells (lane 1) and GP+envAm12 (lane 2) was resolved by electrophoresis, blotted to a nylon membrane, and hybridized with a probe specific for EGFP.