Figure 1: The L1 retrotransposon vector. (A) Schematic diagrams of the S/MAR-based L1 episomal cassettes (pS/MAR-L1-GFP) used for generating loss-of-function genes in ES cells. The vector arrangement ensures that GFP will become functional only after the successful insertion of an L1 copy into a gene. (B) PCR analysis of ES cell genomic DNA. The 1.49 kb PCR product represents the original L1 vector harboring the intron-containing GFP. The 531 bp PCR product, a diagnostic for the loss of the intron, indicates a gene disruption. Positive, 10 ng vector; Negative, no template; Marker, 1 kb-plus DNA marker; U, undifferentiated; D, differentiated ES clone. (C) A representative result of ES clone screening by GFP expression.