FIG. 6.

Southern blots of products of hygromycin retargeting and G418 selection. (A) Hygromycin retargeting. DNA was digested with XbaI and EcoRV and then probed with probe B. Nontargeted clones (+/−) produced one 16-kb band (middle two lanes). Heterozygous clones (+/h) generated one 16-kb wild-type band and one 3.3-kb mutant band (two outside lanes) because the hygromycin cassette introduced a new EcoRV site. (B) G418 selection. DNA was digested with XbaI and then probed with probe B (Fig. 1). All of the clones produced two bands (16-kb wild-type and 3-kb mutant bands), indicating that they were still heterozygous.