Alleles of the microsomal steroid sulfatase gene (Sts) in the pseudoautosomal region of the heterosomes of the mouse.

The gene (Sts) for microsomal steroid sulfatase (STS-EC 3.1.6.2) is located at the distal end of the pseudoautosomal region of the mouse heterosomes. A new improved method was developed to measure the activity of this enzyme in four inbred strains of laboratory mice, their respective congenics for the non pseudoautosomal region of the Y chromosome and their F1s were employed. The method was shown to be highly reliable (.95). No sexual dimorphism was shown but a polymorphism for the enzymatic activity, corresponding to three functional allelic forms was found. The results presented here are compatible with the location of the Sts gene on the X-Y pseudoautosomal region. The underdominance that appears in the F1s, in one set of strains and the difference between reciprocal F1s in the other set must be interpreted cautiously since it is the enzymatic activity which is only measured and not the protein itself. A complex mechanism, involving the gene responsible for the enzyme located on the pseudoautosomal region and autosomal locus or loci which regulate(s) its activity, is suggested as being responsible for the results obtained with the F1s.