Figure 1

Plasmids with an FR containing more than 20 EBNA1 binding sites form minute colonies under selection. The indicated plasmids were transfected into 293/EBNA1 cells, which were subjected to puromycin selection for 18 days in colony formation assays as described in the Materials and Methods section. Representative images of methylene blue stained colonies are shown. The identity of the transfected plasmid is indicated above each image, and the number of EBNA1 binding sites present in the FR of each plasmid is indicated below each image. As a negative control, an assay was also performed with AGP83, a DS-only plasmid that replicates transiently, but is not partitioned, and forms colonies with very low efficiency. The colonies formed from cells transfected with AGP81 and AGP82 did not increase in size even after several weeks of growth in selective media. The number of colonies formed in such assays that were 2 mm in size and larger is indicated in Table 1.