Fig. 1.

Generation of the β-MHC fusion allele. (Top) WT β-MHC gene (upper line) and targeting construct (lower line). (Middle) Targeted allele in ES cells. (Bottom) YFP–β-MHC fusion allele after germline transmission. Open boxes represent 5′ UTRs, and solid boxes represent translated exons. The coding sequence of YFP is shown as a shaded box within exon 4, and loxP sites are shown as triangles. A selection cassette (23) containing a testis promoter-driving CRE (tACE-CRE) and a Neo gene is inserted into intron 1; the selection cassette is not drawn to scale.