LoxP sites were inserted around exons 3-5 and an IRES-nls-eYFP, lox511 flanked stop signal, luciferase gene and FRT flanked selection cassette were inserted downstream of exon 5 via homologous recombination. Flp mediated recombination removed the selection cassette. Cre mediated recombination reomved exons 3-5 and the lox511 flanked stop signal creating a null allele and allowing expression of luciferase.