To eliminate all possible splice variants, exon 7, which contains the first common methionine present in the shortest splice variant, as well as exon 8, which encodes part of the C2 domain, were replaced with a neomycin resistance gene placed in the opposite orientation. Immunoblot of brain homogenates at P5 demonstrated that protein is abolished in mutants. Overexposure of the immunoblot showed a smear present at less than 2% of wild-type levels, likely made up of protein products resulting from cryptic start sites downstream of the deleted sequence.