A 1.2 kb region of the gene spanning part of exon 5, intron 5, exon 6, and part of exon 6 was replaced with a neo resistance cassette via homologous recombination thus deleting the active site of exon 6 and results in the loss of protein cross-linking activity. Western blot of liver, thymus, brain, and erythrocyte samples and RT-PCR analysis of thymus from homozygous mutant animals verified the absence of gene expression. However, residual enzyme activity was detected in some tissues which the authors speculate may be attributed to Tgase1.