Crossing Fosl1tm2Wag with mice expressing Cre in the embryo proper created this allele in which the floxed region containing exons 3 and 4 (containing the dimerization and the DNA-binding domains) was excised. Upon excision, the 3' GFP was spliced to the N-terminal part of the transcript and was thereby activated. Western blot detected the fusion protein using an anti-GFP antibody. Immunofluorescence confirmed GFP activation. (J:93053)