The entire coding region and 1 kb of the 3' UTR were replaced with a lacZ gene and a floxed PGK-neo cassette via homologous recombination. Cre mediated recombination removed the neo cassette. RT-PCR, in situ hybridization and western blot analysis confirmed the absence of RNA and protein expression in homozygous mice. Beta-galactosidase expression is detected in neurons in the cortex, dentate gyrus, striatum and cerebellum where the endogenous protein is highly expressed. Expression of beta-galactosidase is targeted to the nucleus. (J:164148)