FIG. 2.

Targeting the murine WRN locus. (a) Restriction map of a WRN lambda genomic clone (top map) or the mouse WRN-targeting construct (bottom map). The position of an exon encoding the 3′-most region of the helicase domain is indicated by a hatched box. The direction of transcription, as revealed by genomic sequencing, as well as the position of 5′ and 3′ probes used to genotype ES clones and mice are indicated. (b) Genotyping of a litter derived from a heterozygous cross. Hybridization was performed with the 5′ probe as indicated in Fig. 2a. (c) Cells derived from mutant animals do not express any detectable WRN protein. Extracts from ear fibroblasts from mice of the indicated genotypes were probed with chicken affinity-purified anti-WRN antibody. Similar results were obtained probing extracts derived from ES cells of various genotypes (data not shown).