FIG. 4.
G418r foci must arise by trans complementation. (A) The low-level rescue of RD-L1s cannot be accounted for by DNA recombination. An allele of JM101/L1.3 that lacked both the 5′ UTR and the CMV promoter (ΔΔJM101/L1.3) was transfected into HeLa cells alone or with a wild-type allele of L1.3 that lacked the mneoI indicator cassette, and retrotransposition was assayed as described in Fig. 3. The rationale for this experiment is described in the text. JM101/L1.3 and JM105/L1.3 were used as appropriate positive and negative controls. (B) Constructs used in the study. The structure of L1.3 ORF1mneoI is shown, and the rationale for the experiment is described in the text. (C) The resultant G418r foci have the predicted structure. PCR experiments using the oligonucleotides depicted in Fig. 4B (indicated by converging arrows) revealed that the retrotransposed mneoI cassette lacked the intron and was linked physically to L1.3 ORF1. The details of the experiment are provided in the text.