Fig. 1. Structure and expression of Lig 1 targeted alleles. The structure of the 3' end of the wild-type and Lig 1 targeted alleles is shown schematically. Lig 1 exons are depicted as numbered open boxes. In the Lig 1^-(#53) allele, exons 23-27 have been replaced by the PGK-HPRT(RI) Hprt minigene. Hprt exons are shown as numbered closed boxes with the Pgk promoter cross-hatched. In the Lig 1^-(#12) allele, exons 23-27 have been replaced by the DWM110 Hprt minigene, with the Hprt promoter stippled. The normal RNA splicing pattern for Lig 1 mRNA is indicated and the sequences present in the Lig 1/Hprt fusion transcripts from the Lig 1 targeted alleles are shown. Note that the fusion transcript from the Lig 1^-(#53) allele is rare.