Knock-in construct in which a portion of a cDNA corresponding to exons 5-19 followed by a polyadenylation signal was inserted into the endogenous locus. This allele carried a point mutation in codon 644 that altered the corresponding amino acid from lysine to glutamine. A loxP flanked neomycin cassette also inserted downstream of the inseted cDNA was removed via Cre mediated recombination in the final allele. (J:52438)