A phosphoglycerate kinase (PGK) promoter-driven neomycin cassette replaced most of the exon 2 region. Northern and Western blot analysis as well as immunohistochemistry confirmed the absence of full-length (2.6 kB) transcription and 97kD translation products. However, the expression of a shorter 60kD isoform was retained in mutant mice, and this isoform appeared to be translated from an alternatively spliced trancript that did not contain exon 2. Western and GST pull-down analysis of brain lysates demonstrated that the expression of the 60kD isoform was increased 5-fold in mutant mice.