Disruption of the mouse BUBR1 locus. (A) Schematic representation of the structure of mouse BUBR1 showing the relative positions and sizes of the 23 exons (filled boxes). (B) Structures of the wild-type (WT) and mutant BUBR1 loci. SA-Neo-pA denotes a splice acceptor sequence fused to the neomycin resistance gene followed by a polyadenylation signal sequence. PGK-BTK-SD denotes PGK gene promoter fused to BTK gene that is flanked by an SD sequence at its 3′ terminus. The positions and relative orientations of 4 PCR primers (A, B, LTR2, and C) used for genotyping are shown. (C) Genotyping of mouse tail DNA by nested PCR. Genomic DNA isolated from the tails of offspring of crosses between wild-type and BUBR1^+/– mice was analyzed by PCR with primers A, B, and LTR2 (top panel), and the resulting products were subjected to a second round of PCR with primers LTR2 and C.