Fig. 1. Structure of the XA024 gene-trap insertion. Upper, schematic representation of exon 1, intron 1 and exon 2, of the wild-type SUMO1 gene showing the positions of forward primers (arrowheads) used for long-range PCR to localize the insertion. The sequence at the junction between intron 1 and exon 2 is shown (intron in small and exon in capital letters). The position of the insertion and the region of intron 1 deleted in the gene-trap allele are indicated. Middle, structure of the gene trap allele showing inserted vector and reverse primer used for long range PCR. The sequence at the junction of the inserted vector and exon 2 is shown (gene trap vector in small and exon in capital letters); the first nucleotide of exon 2 is lost. Lower, structure of the gene trap vector; the majority was retained in the insertion event.