An isoform specific disruption was achieved by the insertion of a promoterless neomycin selection cassette into exon 3 via homologous recombination. Whereas gamma1 transcript was undetected by RT-PCR analysis of homozygous mutant mice, gamma2 mRNA was readily amplified. An RNAse protection assay further indicated the absence of the gamma1 isoform. (J:42773)