This phenotypic mutant arose spontaneously in a BALB/c colony obtained from Harlan. A B2 element is inserted in exon 7 near the 3' splice site at position 861 of the mRNA. This generates an in-frame stop codon and changes the Ile at residue 260 to 260-ArgAspTrp-262 as well inserting a 15bp duplication of the mRNA sequence from nucleotide 846 to 860. (J:78078, J:96427)