Differential effects of molybdate on the hydrodynamic and DNA-binding properties of the non-activated and activated forms of the androgen receptor in calf uterus.

Calf uterine cytosol contains an androgen receptor with a relative molecular mass of approx. 90,000. In this study we have analysed the structure and aggregation properties of the androgen receptor, using sucrose density gradient centrifugation on a vertical rotor (VTi65). In the presence of 10 mM NaCl the androgen receptor in whole cytosol sedimented at 8 S irrespective of the presence of molybdate. In 400 mM NaCl the receptor dissociated to a 4.3 S entity. In whole cytosol molybdate promoted a partial shift of the 4.3 S receptor into the aggregated 8 S state. The time of exposure of the receptor to molybdate and NaCl determined the proportion of receptor sedimentating at 8 S and 4.3 S. The DNA-binding form of the uterine androgen receptor when analysed under the conditions of the DNA-cellulose binding assay, sedimented at 6.5 S. Increasing concentrations of molybdate shifted its sedimentation coefficient gradually from 6.5 S to 4.5 S and in parallel reduced the DNA-binding capacity. Molybdate added to a partially purified, DNA-binding form of the androgen receptor did not promote receptor aggregation to faster sedimentating forms. This suggests that such preparations are devoid of an androgen receptor-aggregation factor. Indirect evidence for such a factor was obtained from reconstitution experiments with whole cytosol. Our results indicate that the DNA-binding form of the androgen receptor interacts with a cytosol factor to form the 8 S receptor complex. Molybdate has diverse effects: in the presence of the cytosol factor it stabilizes the 8S complex; in its absence molybdate prevents in a concentration-dependent way DNA-binding as well as reaggregation of the monomeric 4.3 S form.