Exons 2 to 5 were replaced with a lacZ (galactosidase) reporter gene containing a mouse nuclear localization signal (NLS) followed by two downstream polyadenylation signals (pA) and a, FRT-flanked PGK-neomycin selection marker in reverse direction. The neomycin selection cassette was removed via Flp-mediated recombination. (J:257948)