Part of exon 3 was replaced with a modified version of a yellow fluorescent protein gene (Venus) and a floxed pgk-neo cassette was inserted in intron 3 via homologous recombination. The neo cassette was then removed by Cre mediated recombination. RT-PCR and autoradiogram analysis confirmed the absence of RNA expression and binding activity in brains from homozygous mice. (J:146587)