A bacterial lacZ-neomycin fusion gene was inserted into the gene to replace a 608 bp portion of exon 3 of the gene , encoding thr-38 to glu-299, such that the endogenous gene promoter drives expression of beta-galactosidase. Beta-galactosidase expression from this allele is detectable in the immune system, including the spleen and lymph nodes and in coagulating glands of the male reproductive system. (J:135850)