A targeting vector containing an FRT-flanked PGK-NEO cassette, a DTA cassette and a Cre recombinase cassette are used to replace the start codon in exon 1 and 59 bp of signal peptide sequence at the ATG start codon. Flp-mediated recombination removed the FRT-flanked neo cassette. Immunostaining analysis of the suprachiasmatic nucleus does not detect a gene product. The investigator reports that the Cre recombinase cassette is non-functional or very minimally functional. (J:219926)