Kras^tm3Tyj

Insertion of the targeting vector results in a duplication of exon 1 with a neomycin resistance gene cassette between the duplicate exons. Both copies of exon 1 contain an activating glycine to aspartic acid mutation at codon 12 (p.G12D). In the absence of intrachromosomal recombination, this allele does not produce any protein and mutant homozygotes die during embryogenesis. In heterozygotes, when intrachromosomal recombination occurs in vivo, all of the recombination events produce an active p.G12D allele. Expression of G12D protein results in the formation of lung tumors and death at ~200 days (7 months). (J:68981)