Genotyping of mice. Three primers were used to distinguish wild-type and mutant alleles of Trip13: primer 1, 5′-CGTCGCTCCATTGCTTTGTGC-3′; primer 2, 5′-AGTAGTGGTACACTGTATTTTTGCTTTCATTGA-3′; and primer 3, 5′-GTAGATCCCGGCGCTCTTACCAA-3′. Primers 1 and 2 are located upstream and downstream, respectively, of the gene trap insertion within the intron 3. Primer 3 corresponds to pGTlxf sequence. Primers 1 and 2 amplify a 700-bp band from a wild-type allele; primers 1 and 3 amplify a 540-bp fragment from a mutant allele. Separate reactions were used to assay the presence or absence of each amplicon from a DNA sample. The cycling conditions were: 94 °C 2 min; 35 cycles of 94 °C 30 s, 57 °C 45 s, and 72°C 50 s; and 72 °C 2 min.