A cysteine to alanine missense mutation was generated at codon 64 (C64A) in exon 2 by site directed mutagenesis. An artifactual loxP site remained in intron 2 after the floxed neo selection cassette was removed by in vitro cre mediated recombination. The incorporation of the missense mutation was confirmed by sequence analysis and protein levels similar to those of wild-type were detected by Western blot anlaysis of homozygous mutant mice. (J:83750)