FIG. 3.

Equal numbers of GFP expression-normalized wild-type and mutant TS-expressing K562 cells were sorted by FACS and cultured for 14 days (a) under standard cell culture conditions and (b) in medium supplemented with 500 nM 5-FUdR. Genomic DNA extracted from cells after 0, 3, 7, and 14 days of culture was used as template in PCRs employing primers that selectively amplified the retrovirally transduced TS genes. The resulting amplicons were cloned into the pCR 4-TOPO vector and transformed into DH5α Escherichia coli DH5α. The bacteria were plated and incubated overnight, and plasmids from the resultant colonies (n: 150 for each time point) were DNA sequenced with primers flanking the TS gene sequence.