Marker gene expression from constitutive or erythroid-specific promoters in maturing erythroblasts. (A) Schematic representation of the lentiviral vectors encoding for expression of GFP from the MSCV, ankyrin-1, or β-spectrin promoters. The PRE element is not present in the MSCV vector. (B) GFP expression by erythroblasts derived from CD34⁺ cells transduced with vectors having the MSCV, spectrin, or ankyrin promoter after various times after transduction where the percentages and MFI are indicated for the proportion of cells considered positive. The percentage of glycophorin A-positive cells at the same time points are shown above the GFP profiles. (C) Southern blot analysis of genomic DNA extracted from transduced cells, digested with BglII, an enzyme that cuts twice within the vector genome and probed with an RRE fragment common to all vectors from the 5′ end of the genome. DNA size marker is shown in the leftmost lane (vertical lines have been inserted to indicate where lanes have been repositioned). Numbers below each lane on the image represent the VCN as determined by densitometry analysis, relative to controls 1.0 or 0.5, which consist of DNA from a K562 clone that contains a single copy of an integrated lentiviral vector either used directly (1.0) or diluted 1:1 with native K562 DNA to establish a sample with a copy number of 0.5.