Figure 1.

Targeted disruption of mouse TOP3β gene. (Upper) Sketches of the relevant regions of the targeting vector pKYK100, the endogenous TOP3β locus, and the expected Δtop3β allele. B, E, K, S, and X denote BglI, EcoRI, KpnI, SacI, and XbaI restriction sites, respectively. The 5′ and 3′ probes used in genotyping were derived from regions depicted under the Δtop3β allele. (Lower) Representative results of genotyping by Southern blot hybridization; the 5′ probe was used in this experiment.