Exons 1-2 and part of exon 3 were replaced with neomycin resistance gene via homologous recombination. This region of the gene encodes amino acids 1-413 and contains the translation start site, a regulatory domain that controls calmodulin-dependent cytoplasmic-to-nuclear translocation, and part of the DNA-binding domain. Western blot and RNase protection assay of homozygous mutant embryos verified the absence of gene expression. (J:70266)