A bacterial lacZ gene was inserted into the gene such that the endogenous gene promoter drives expression of beta-galactosidase. The highest levels of RNA transcripts are detectable in lymph nodes and adrenal gland. Moderate levels of RNA transcripts are detectable in lung, spleen, thymus, skin, gallbladder, urinary bladder, pituitary gland, testis, epididymis, prostate gland, ovary, uterus and white fat. LacZ expression was detected in: brain, thymus, spleen, lymph nodes, bone marrow, aorta, heart, lung, pancreas, kidney, urinary bladder, thyroid gland, skeletal muscle, skin, testis, prostate gland, ovary and uterus.