A cassette of the sequence corresponding to the exons 6 and 7 of the Zf423 gene with the nucleotides 3861-4108 of the ORF deleted and an FRT flanked neomycin selection cassette replaced the endogenous exons 6 and 7. It causes a frameshift mutation that produces a stop codon 158 bp into exon 8. The resulting C-termally trancated protein lacks zinc fingers 28-30 and 91 C-terminal amino acids. (J:245759)