A codon-improved cre recombinase gene, preceded by a 5-codon linker sequence and followed by an SV40 intron and poly(A) signal sequences, was inserted immediately after the endogenous start codon in exon 1. Point mutations were introduced into exon 2 of the Il17a gene to disable an internal ATG-site. The neomycin resistance gene cassette that was inserted downstrea of the cre gene was excised by FLPe-mediated recombination to generate the the final allele. (J:169305)