A stop codon (TAG) replaced the codon for Leu710 (TTA) (L710X), truncating the last 36 residues that are important for binding to protein kinase A (PKA). A loxP-flanked neomycin resistance cassette was also inserted downstream of the lone coding exon. After germ line transmission, the neomycin resistance cassette was removed by crossing with cre-transgenic mice. Western blots for PKA subunits from postsynaptic densities of the forebrain indicated reduced levels of protein, confirming mutation of the targeted gene.