The androgen receptor of the testicular-feminized (Tfm) mutant mouse is smaller than the wild-type receptor

The physicochemical and immunological properties of androgen receptors from kidney and brain of testicular-feminized (Tfm) mutant mice and wild-type mice were compared. Analysis by gel filtration and sucrose density gradients revealed that the mol wt of the mutant receptor was 66K (38A; 3.8S) which was significantly smaller than the 110K (53A; 4.6S) size of the wild-type androgen receptor (P less than 0.05). Mixing experiments failed to demonstrate any role for differential proteolysis in the size differences between these receptors. Interaction of the mutant androgen receptor with specific polyclonal antiandrogen receptor antibodies produced significantly smaller immune complexes than that formed with wild-type receptor (12S vs. 17S; P less than 0.01). This confirmed the smaller size of the Tfm mutant androgen receptor and suggested that it contained fewer epitopes. The Tfm kidney cytosols also demonstrated a decreased concentration of androgen receptor-binding activity relative to that of the wild type. Together, these results suggest that the androgen insensitivity associated with the Tfm phenotype is due to a deficiency of androgen receptor in target tissues and a qualitative defect in the androgen receptor protein itself.