ES cell containing Fosl2tm2Wag were transfected with a cre-expressing plasmid to remove the exons 3 and 4 along with a neo cassette. RNase protection and western blot were used to confirm the absence of full-length protein from mouse embryonic fibroblasts using an anti-Fosl2 antibody. However, a fusion protein with the remaining GFP open reading frame is detected using an anti-GFP antibody. (J:125028)