The insertion of a neomycin selection cassette into exon 6 introduced a stop codon that precludes translation of the essential zinc finger DNA-binding domain. Northern blot analysis of total embryonic RNA showed the presence of longer transcripts, resulting from the insertion of neo. Western blot analysis using an anti-serum directed against the amino terminus of the encoded protein confirmed the presence of a truncated protein in extracts from homozygous mutant embryos. (J:39865)