A nucleotide substitution resulting in the amino-acid substitution of the fourth cysteine to phenylalanine in exon 7 was knocked into the open reading frame along with a floxed neo cassette that was subsequently removed by germ line, cre-mediated recombination. The absence of saposin B was confirmed by western blot analysis on liver extracts but the expression of saposin A, C and D (the other forms post-translationally generated from this locus) was not affected. (J:137650)